<PAGE>
--------------------------------------------------------------------------------
--------------------------------------------------------------------------------
 
                       SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549
 
                            ------------------------
 
                                    FORM 8-K
                                 CURRENT REPORT
 
     Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934
                                  MAY 11, 2001
                Date of Report (Date of earliest event reported)
 
                            ------------------------
 
                              SONUS NETWORKS, INC.
             (Exact Name of Registrant as Specified in its Charter)
 

<TABLE>
<CAPTION>
          DELAWARE                       000-30229                     04-3387074
-----------------------------  -----------------------------  -----------------------------
<S>                            <C>                            <C>
(State or Other Jurisdiction                                          (IRS Employer
      of Incorporation)          (Commission File Number)          Identification No.)
</TABLE>

 
                 5 CARLISLE ROAD, WESTFORD, MASSACHUSETTS 01886
 
              (Address of Principal Executive Offices) (Zip Code)
 
                                 (978) 692-8999
 
              (Registrant's telephone number, including area code)
 
--------------------------------------------------------------------------------
--------------------------------------------------------------------------------

<PAGE>

ITEM 5. OTHER EVENTS.
 
    On May 11, 2001, the stockholders of Sonus voted to approve an amendment to
the Fourth Amended and Restated Certificate of Incorporation of Sonus increasing
the number of shares of common stock Sonus is authorized to issue from
300,000,000 shares to 600,000,000 shares. The Certificate of Amendment is
attached as an exhibit hereto and is incorporated by reference.
 
    Sonus is filing the audited consolidated financial statements of telecom
technologies, inc., or TTI, as of December 31, 1999 and 2000, and for TTI's
fiscal years ended December 31, 1998, 1999 and 2000, and the unaudited pro forma
condensed combined financial information of Sonus and TTI for the year ended
December 31, 2000 and three months ended March 31, 2001; each attached as an
exhibit hereto, and is incorporating such financial information herein by
reference.
 

ITEM 7. EXHIBITS.
 

<TABLE>
<CAPTION>
EXHIBIT
NUMBER   DESCRIPTION
-------  -----------
<S>      <C>
23.1     Consent of Arthur Andersen LLP relating to consolidated
         financial statements of telecom technologies, inc.
99.1     Consolidated financial statements of telecom technologies,
         inc.
99.2     Unaudited pro forma condensed combined financial
         information.
99.3     Certificate of Amendment to Sonus Networks, Inc.'s Fourth
         Amended and Restated Certificate of Incorporation.
</TABLE>

 

                                   SIGNATURE
 
    Pursuant to the requirements of the Securities Exchange Act of 1934, the
Registrant has duly caused this report to be signed on its behalf by the
undersigned hereunto duly authorized.
 

<TABLE>
<S>                                                    <C>  <C>
Date: June 20, 2001                                    SONUS NETWORKS, INC.
 
                                                       By:             /s/ STEPHEN J. NILL
                                                            -----------------------------------------
                                                                         Stephen J. Nill
                                                            Chief Financial Officer, Vice President of
                                                             Finance and Administration and Treasurer
                                                               (Principal Financial and Accounting
                                                                             Officer)
</TABLE>

 

<PAGE>

                                 EXHIBIT INDEX
 

<TABLE>
<CAPTION>
EXHIBIT
  NO.    DESCRIPTION
-------  -----------
<S>      <C>
23.1     Consent of Arthur Andersen LLP relating to consolidated
         financial statements of telecom technologies, inc.
99.1     Consolidated financial statements of telecom technologies,
         inc.
99.2     Unaudited pro forma condensed combined financial
         information.
99.3     Certificate of Amendment to Sonus Networks, Inc.'s Fourth
         Amended and Restated Certificate of Incorporation.
</TABLE>






<PAGE>
                                                                    EXHIBIT 23.1
 
                   CONSENT OF INDEPENDENT PUBLIC ACCOUNTANTS
 
As independent public accountants, we hereby consent to the incorporation of our
report dated March 5, 2001 (except with respect to the matter discussed in
Note 2 as to which the date is June 6, 2001) on the consolidated financial
statements of telecom technologies, inc. included in this current report on
Form 8-K, into Sonus Networks, Inc.'s previously filed Registration Statement on
Form S-3 (File No. 333-61940).
 
                                          /s/ Arthur Andersen LLP
 
Boston, Massachusetts
June 20, 2001





<PAGE>
                                                                    EXHIBIT 99.1
 
                           TELECOM TECHNOLOGIES, INC.
                   INDEX TO CONSOLIDATED FINANCIAL STATEMENTS
 

<TABLE>
<CAPTION>
                                                                PAGE
                                                              --------
<S>                                                           <C>
Report of Independent Public Accountants....................     F-2
 
Consolidated Balance Sheets.................................     F-3
 
Consolidated Statements of Operations.......................     F-4
 
Consolidated Statements of Redeemable Common Stock and
  Stockholders' Deficit.....................................     F-5
 
Consolidated Statements of Cash Flows.......................     F-6
 
Notes to Consolidated Financial Statements..................     F-7

</TABLE>

 
                                      F-1

<PAGE>

                    REPORT OF INDEPENDENT PUBLIC ACCOUNTANTS
 
To the Board of Directors and Stockholder of
telecom technologies, inc.:
 
We have audited the accompanying consolidated balance sheets of telecom
technologies, inc. (a Texas corporation) as of December 31, 1999 and 2000, and
the related consolidated statements of operations, redeemable common stock and
stockholders' deficit and cash flows for the years ended December 31, 1998, 1999
and 2000. These consolidated financial statements are the responsibility of the
telecom technologies, inc. management. Our responsibility is to express an
opinion on these consolidated financial statements based on our audits.
 
We conducted our audits in accordance with auditing standards generally accepted
in the United States. Those standards require that
 we plan and perform the audit
to obtain reasonable assurance about whether the financial statements are free
of material misstatement. An audit includes examining, on a test basis, evidence
supporting the amounts and disclosures in the financial statements. An audit
also includes assessing the accounting principles used and significant estimates
made by management, as well as evaluating the overall financial statement
presentation. We believe that our audits provide a reasonable basis for our
opinion.
 
In our opinion, the financial statements referred to above present fairly, in
all material respects, the financial position of telecom technologies, inc. as
of December 31, 1999 and 2000, and the results of its operations and its cash
flows for the years ended December 31, 1998, 1999 and 2000 in conformity with
accounting principles generally accepted in the United States.
 
                                          /s/ Arthur Andersen LLP
 
Boston, Massachusetts
March 5, 2001

(except with respect to the matter discussed
in Note 2 as to which the date is June 6, 2001)
 
                                      F-2

<PAGE>
                           TELECOM TECHNOLOGIES, INC.
                          CONSOLIDATED BALANCE SHEETS
                       (IN THOUSANDS, EXCEPT SHARE DATA)
 

<TABLE>
<CAPTION>
                                                                 DECEMBER 31,
                                                              -------------------
                                                                1999       2000
                                                              --------   --------
<S>                                                           <C>        <C>
                                     ASSETS
CURRENT ASSETS:
  Cash and cash equivalents.................................  $   533    $    586
  Accounts receivable, net of allowance of $150 and $400 at
    December 31, 1999 and 2000, respectively................    5,587       2,128
  Inventories...............................................    2,410       4,191
  Deferred tax asset........................................      399         399
  Income tax receivable.....................................      740         780
  Other current assets......................................      292         210
                                                              -------    --------
      Total current assets..................................    9,961       8,294
 
PROPERTY AND EQUIPMENT, net of accumulated depreciation and
  amortization..............................................    2,122       4,718
 
OTHER ASSETS................................................      799          --
                                                              -------    --------
                                                              $12,882    $ 13,012
                                                              =======    ========
 
         LIABILITIES, REDEEMABLE COMMON STOCK AND STOCKHOLDERS' DEFICIT
CURRENT LIABILITIES:
  Note payable to bank......................................  $ 4,000    $  7,000
  Accounts payable..........................................    2,489       4,862
  Accrued expenses..........................................    1,685       4,422
  Deferred revenue..........................................    2,430       2,977
  Current portion of capital lease obligations..............      192         553
                                                              -------    --------
      Total current liabilities.............................   10,796      19,814
 
CAPITAL LEASE OBLIGATIONS, less current portion.............      673       1,292
 
COMMITMENTS (Note 7)
 
REDEEMABLE COMMON STOCK, no par value:
  Issued and outstanding--7,777,780 shares of Class A voting
    common stock and 2,222,220 shares of Class B non-voting
    common stock, at redemption value (Note 8)..............    7,226      50,500
 
STOCKHOLDERS' DEFICIT:
  Class A voting common stock, no par value:
    Authorized--180,000,000 shares
    Issued and outstanding--70,000,000 shares...............        1           1
  Class B non-voting common stock, no par value:
    Authorized--50,000,000 shares
    Issued and outstanding--20,000,000 shares...............       --          --
  Capital in excess of par value............................       --      10,993
  Accumulated deficit.......................................   (5,814)    (60,542)
  Deferred compensation.....................................       --      (9,046)
                                                              -------    --------
      Total stockholders' deficit...........................   (5,813)    (58,594)
                                                              -------    --------
                                                              $12,882    $ 13,012
                                                              =======    ========
</TABLE>

 
  THE ACCOMPANYING NOTES ARE AN INTEGRAL PART OF THESE CONSOLIDATED FINANCIAL
                                  STATEMENTS.
 
                                      F-3

<PAGE>
                           TELECOM TECHNOLOGIES, INC.
                     CONSOLIDATED STATEMENTS OF OPERATIONS
                     (IN THOUSANDS, EXCEPT PER SHARE DATA)
 

<TABLE>
<CAPTION>
                                                                  YEAR ENDED DECEMBER 31,
                                                              --------------------------------
                                                                1998        1999       2000
                                                              ---------   --------   ---------
<S>                                                           <C>         <C>        <C>
REVENUES:
  Product...................................................  $  6,012    $ 9,846    $ 21,264
  Professional services.....................................     8,732      9,486       7,367
                                                              --------    -------    --------
      Total revenues........................................    14,744     19,332      28,631
Cost of product and services(1).............................    11,083     11,637      14,381
                                                              --------    -------    --------
GROSS PROFIT................................................     3,661      7,695      14,250
 
OPERATING EXPENSES:
  Research and development(1)...............................     1,389      7,486      14,735
  Sales and marketing(1)....................................     1,183      3,287       5,090
  General and administrative(1).............................     1,344      1,960       3,586
  Stock-based compensation..................................        --         --       1,947
                                                              --------    -------    --------
      Total operating expenses..............................     3,916     12,733      25,358
                                                              --------    -------    --------
LOSS FROM OPERATIONS........................................      (255)    (5,038)    (11,108)
 
OTHER INCOME (EXPENSE):
  Interest expense..........................................      (188)      (132)       (511)
  Interest income...........................................        25         58         118
  Sale of product line......................................        --      5,500          --
  Other income..............................................         8        815          47
                                                              --------    -------    --------
INCOME (LOSS) BEFORE INCOME TAXES...........................      (410)     1,203     (11,454)
Provision (benefit) for income taxes........................      (145)       336          --
                                                              --------    -------    --------
NET INCOME (LOSS)...........................................  $   (265)   $   867    $(11,454)
                                                              ========    =======    ========
PER SHARE INFORMATION:
  Basic and diluted net income (loss) per share
  (Note 1(n))...............................................  $  (0.00)   $  0.01    $  (0.11)
                                                              ========    =======    ========
  Shares used in computation................................   100,000    100,000     100,000
                                                              ========    =======    ========
------------------------
 
(1) Excludes non-cash stock-based
  compensation expense as follows:
 
     Cost of product and services...........................                         $     35
     Research and development...............................                               82
     Sales and marketing....................................                            1,429
     General and administrative.............................                              401
                                                                                     --------
                                                                                     $  1,947
                                                                                     ========
</TABLE>

 
    THE ACCOMPANYING NOTES ARE AN INTEGRAL PART OF THESE CONSOLIDATED FINANCIAL
STATEMENTS.
 
                                      F-4

<PAGE>
                           TELECOM TECHNOLOGIES, INC.
  CONSOLIDATED STATEMENTS OF REDEEMABLE COMMON STOCK AND STOCKHOLDERS' DEFICIT
                       (IN THOUSANDS, EXCEPT SHARE DATA)

<TABLE>
                                                                                     COMMON STOCK
                                    CLASS A AND B         -------------------------------------------------------------------
                                      REDEEMABLE
                                     COMMON STOCK              ORDINARY                CLASS A                 CLASS B
                               ------------------------   -------------------   ---------------------   ---------------------
                                            REDEMPTION                PAR                     PAR                     PAR
                                 SHARES       VALUE       SHARES     VALUE        SHARES     VALUE        SHARES     VALUE
                               ----------   -----------   --------   --------   ----------   --------   ----------   --------
<S>                            <C>          <C>           <C>        <C>        <C>          <C>        <C>          <C>
BALANCE, DECEMBER 31, 1997...       2,000     $   949      18,000     $   1             --    $  --             --     $ --
  Reorganization.............   9,998,000          --     (18,000)       (1)    70,000,000        1     20,000,000       --
  Accretion of increase in
    value of redeemable
    common stock.............          --       1,332          --        --             --       --             --       --
  Net loss...................          --          --          --        --             --       --             --       --
                               ----------     -------     -------     -----     ----------    -----     ----------     ----
BALANCE, DECEMBER 31, 1998...  10,000,000       2,281          --        --     70,000,000        1     20,000,000       --
  Accretion of increase in
    value of redeemable
    common stock.............          --       4,945          --        --             --       --             --       --
  Net income.................          --          --          --        --             --       --             --       --
                               ----------     -------     -------     -----     ----------    -----     ----------     ----
BALANCE, DECEMBER 31, 1999...  10,000,000       7,226          --        --     70,000,000        1     20,000,000       --
  Accretion of increase in
    value of redeemable
    common stock.............          --      43,274          --        --             --       --             --       --
  Deferred compensation
    related to stock
    option grants............          --          --          --        --             --       --             --       --
  Amortization of deferred
    compensation.............          --          --          --        --             --       --             --       --
  Compensation related to
    stock options granted
    to non-employees.........          --          --          --        --             --       --             --       --
  Net loss...................          --          --          --        --             --       --             --       --
                               ----------     -------     -------     -----     ----------    -----     ----------     ----
BALANCE, DECEMBER 31, 2000...  10,000,000     $50,500          --     $  --     70,000,000    $   1     20,000,000     $ --
                               ==========     =======     =======     =====     ==========    =====     ==========     ====
 
<S>                            <C>         <C>            <C>             <C>
                               CAPITAL
                                  IN                                        TOTAL
                               EXCESS OF   ACCUMULATED     DEFERRED       STOCKHOLDERS'
                               PAR VALUE    DEFICIT       COMPENSATION     DEFICIT
                               ---------   ------------   -------------   -------------
BALANCE, DECEMBER 31, 1997...   $    --      $   (139)       $    --        $   (138)
  Reorganization.............        --            --             --              --
  Accretion of increase in
    value of redeemable
    common stock.............        --        (1,332)            --          (1,332)
  Net loss...................        --          (265)            --            (265)
                                -------      --------        -------        --------
BALANCE, DECEMBER 31, 1998...        --        (1,736)            --          (1,735)
  Accretion of increase in
    value of redeemable
    common stock.............        --        (4,945)            --          (4,945)
  Net income.................        --           867             --             867
                                -------      --------        -------        --------
BALANCE, DECEMBER 31, 1999...        --        (5,814)            --          (5,813)
  Accretion of increase in
    value of redeemable
    common stock.............        --       (43,274)            --         (43,274)
  Deferred compensation
    related to stock
    option grants............    10,262            --        (10,262)             --
  Amortization of deferred
    compensation.............        --            --          1,216           1,216
  Compensation related to
    stock options granted
    to non-employees.........       731            --             --             731
  Net loss...................        --       (11,454)            --         (11,454)
                                -------      --------        -------        --------
BALANCE, DECEMBER 31, 2000...   $10,993      $(60,542)       $(9,046)       $(58,594)
                                =======      ========        =======        ========
</TABLE>

 
    THE ACCOMPANYING NOTES ARE AN INTEGRAL PART OF THESE CONSOLIDATED FINANCIAL
                                  STATEMENTS.
 
                                      F-5

<PAGE>
                           TELECOM TECHNOLOGIES, INC.
 
                     CONSOLIDATED STATEMENTS OF CASH FLOWS
 
                                 (IN THOUSANDS)
 

<TABLE>
<CAPTION>
                                                                 YEAR ENDED DECEMBER 31,
                                                              ------------------------------
                                                                1998       1999       2000
                                                              --------   --------   --------
<S>                                                           <C>        <C>        <C>
CASH FLOWS FROM OPERATING ACTIVITIES:
  Net income (loss).........................................  $  (265)   $   867    $(11,454)
  Adjustments to reconcile net income (loss) to net
    cash (used in) provided by operating activities:
    Depreciation and amortization...........................       99        324         798
    Deferred income taxes...................................   (2,288)       153          --
    Stock-based compensation................................       --         --       1,947
    Changes in operating assets and liabilities:
      Accounts receivable...................................     (651)    (1,368)      3,459
      Inventories...........................................       11     (1,590)     (1,781)
      Income tax receivable.................................    1,256       (740)        (40)
      Other current assets..................................      423       (176)         82
      Other assets..........................................     (375)      (280)        799
      Accounts payable and accrued expenses.................     (142)     2,464       5,110
      Deferred revenue......................................    1,465        965         547
                                                              -------    -------    --------
        Net cash (used in) provided by operating
        activities..........................................     (467)       619        (533)
                                                              -------    -------    --------
 
CASH FLOWS FROM INVESTING ACTIVITIES:
  Purchases of property and equipment.......................     (743)      (592)     (2,085)
  Cash paid for acquisition.................................       --       (904)         --
                                                              -------    -------    --------
        Net cash used in investing activities...............     (743)    (1,496)     (2,085)
                                                              -------    -------    --------
 
CASH FLOWS FROM FINANCING ACTIVITIES:
  Net proceeds from note payable to bank....................    3,000      1,000       3,000
  Payments on capital lease obligations.....................       --       (110)       (329)
  Payments on related party note............................   (1,660)        --          --
                                                              -------    -------    --------
        Net cash provided by financing activities...........    1,340        890       2,671
                                                              -------    -------    --------
NET INCREASE IN CASH AND CASH EQUIVALENTS...................      130         13          53
CASH AND CASH EQUIVALENTS, BEGINNING OF YEAR................      390        520         533
                                                              -------    -------    --------
CASH AND CASH EQUIVALENTS, END OF YEAR......................  $   520    $   533    $    586
                                                              =======    =======    ========
SUPPLEMENTAL DISCLOSURES OF CASH FLOW INFORMATION:
  Cash paid for income taxes................................  $   600    $ 1,000    $     40
                                                              =======    =======    ========
  Cash paid for interest....................................  $   228    $   147    $    447
                                                              =======    =======    ========
SUPPLEMENTAL DISCLOSURE OF NON-CASH TRANSACTIONS:
  Equipment obtained under capital lease obligations........  $    --    $   975    $  1,309
                                                              =======    =======    ========
  Software contributed in acquisition.......................  $    --    $   150    $     --
                                                              =======    =======    ========
SUPPLEMENTAL DISCLOSURE OF CASH FLOWS RELATED TO
  ACQUISITION:
  Fair value of assets acquired, excluding cash.............  $    --    $ 1,054    $     --
  Software paid as consideration............................       --       (150)         --
                                                              -------    -------    --------
  Cash used for acquisition.................................  $    --    $  (904)   $     --
                                                              =======    =======    ========
</TABLE>

 
    THE ACCOMPANYING NOTES ARE AN INTEGRAL PART OF THESE CONSOLIDATED FINANCIAL
STATEMENTS.
 
                                      F-6

<PAGE>
                           TELECOM TECHNOLOGIES, INC.
 
                   NOTES TO CONSOLIDATED FINANCIAL STATEMENTS
 
(1) OPERATIONS AND SIGNIFICANT ACCOUNTING POLICIES
 
    telecom technologies, inc. (TTI) was incorporated on November 24, 1993 as a
Texas corporation and is a provider of software products and services for
network and service providers, offering end-to-end solutions for next
generation, carrier-grade, multi-service networks. TTI's professional services
include network design and planning, implementation, system integration, testing
and support. On January 18, 2001, Sonus Networks, Inc. (Sonus) acquired TTI (see
Note 2).
 
    The market for TTI's products and services is characterized by rapidly
changing technology, evolving industry standards and new product introductions.
TTI's market is intensely competitive. TTI's success will depend on its ability
to enhance and market existing products and services and introduce new products,
features and services to meet changing customer requirements and evolving
standards.
 
    The accompanying consolidated financial statements reflect the application
of certain significant accounting policies as described in this note and
elsewhere in the accompanying consolidated financial statements and notes.
 
    (A)  PRINCIPLES OF CONSOLIDATION
 
    The accompanying consolidated financial statements include the accounts of
TTI and its wholly owned subsidiary. All material intercompany transactions and
balances have been eliminated.
 
    (B)  CASH EQUIVALENTS
 
    Cash equivalents are stated at cost plus accrued interest, which
approximates market value and have original maturities of three months or less.
 
    (C)  CONCENTRATION OF CUSTOMERS AND CREDIT RISK AND LIMITED SUPPLIERS
 
    Financial instruments that potentially subject TTI to concentrations of
credit risk are cash and cash equivalents and accounts receivable. TTI has no
significant off-balance-sheet concentrations such as foreign exchange contracts,
options contracts or other foreign hedging arrangements. The majority of TTI's
cash is maintained with a commercial bank.
 
    TTI's customers are generally large companies in the United States operating
in the telecommunications industry. Concentration of credit risk with respect to
such customers is limited due to the size and financial strength of those
customers who generally represent individually significant balances. TTI
establishes an allowance for doubtful accounts as necessary based upon factors
surrounding the credit risk of customers, historical trends, and other relevant
information. TTI's receivables are generally unsecured.
 
    Certain software licenses from third-parties used in TTI products are
procured from a single source. The termination of any such license could
interrupt TTI's delivery of products and thereby adversely affect TTI's revenues
and operating results.
 
    For the years ended December 31, 1998, 1999 and 2000, three, two, and two
customers, each of whom contributed more than 10% of revenue, collectively
accounted for an aggregate of 63%, 51%, and 58%, respectively, of TTI's
revenues. As of December 31, 1999 and 2000, two and five customers accounted for
66% and 91%, respectively, of TTI's accounts receivable.
 
    (D)  INVENTORIES
 
    Inventories consist of finished goods and are stated at the lower of cost
(first-in, first-out basis) or market.
 
    (E)  PROPERTY AND EQUIPMENT
 
    Property and equipment are stated at cost, net of accumulated depreciation
and amortization. Expenditures for maintenance and repairs are charged to
expense as incurred, whereas major betterments are capitalized as additions to
property and equipment. TTI records depreciation of property and equipment using
the straight-line method over the estimated useful lives of the assets.
 
                                      F-7

<PAGE>
                           TELECOM TECHNOLOGIES, INC.
 
             NOTES TO CONSOLIDATED FINANCIAL STATEMENTS (CONTINUED)
 
    (F)  REVENUE RECOGNITION
 
    Revenue from software license agreements is recognized upon execution of the
contract and shipment of the software provided that there are no uncertainties
regarding acceptance, persuasive evidence of an arrangement exists, the fee is
fixed or determinable and collection of the related receivable is considered
probable. If uncertainties exist, TTI recognizes revenue when those
uncertainties are resolved. In multiple element arrangements, TTI uses the
residual method of accounting in accordance with Statements of Position 97-2 and
98-9.
 
    Service revenue consists primarily of contract engineering and consulting
services. TTI also provides consulting services to customize its software
products on a contract basis. Services are provided on both a time-and-materials
basis and a fixed fee basis. Revenue with respect to time-and-materials
contracts is recognized as services are provided. Revenue from services on fixed
fee contracts is recognized under the terms of the contract based upon when the
services have been provided and accepted by the customer, if required.
Provisions for losses on service contracts are recorded in the period in which
they first become determinable. Amounts collected prior to satisfying the
revenue recognition criteria are reflected as deferred revenue.
 
    In December 1999, the Securities and Exchange Commission issued Staff
Accounting Bulletin No. 101, REVENUE RECOGNITION IN FINANCIAL STATEMENTS. TTI's
revenue recognition policy complies with this pronouncement.
 
    (G)  SOFTWARE DEVELOPMENT COSTS
 
    TTI accounts for its software development costs in accordance with Statement
of Financial Accounting Standards (SFAS) No. 86, ACCOUNTING FOR THE COSTS OF
COMPUTER SOFTWARE TO BE SOLD, LEASED OR OTHERWISE MARKETED. Accordingly, the
costs for the development of new software and substantial enhancements to
existing software are expensed as incurred until technological feasibility has
been established, at which time any additional costs would be capitalized. TTI
has determined that technological feasibility is established at the time a
working model of the software is completed. Because TTI believes its current
process for developing software is essentially completed concurrently with the
establishment of technological feasibility, no costs have been capitalized to
date.
 
                                      F-8

<PAGE>
                           TELECOM TECHNOLOGIES, INC.
 
             NOTES TO CONSOLIDATED FINANCIAL STATEMENTS (CONTINUED)
 
    (H)  INCOME TAXES
 
    TTI has computed its provision for income taxes using the liability method.
Under the liability method, deferred income tax assets and liabilities are
determined based on differences between financial reporting and income tax bases
of assets and liabilities and are measured using the enacted tax rates and laws.
 
    (I)  STOCK-BASED COMPENSATION
 
    TTI uses the intrinsic value-based method of Accounting Principles Board
(APB) Opinion No. 25, ACCOUNTING FOR STOCK ISSUED TO EMPLOYEES, to account for
its employee stock-based compensation plan and uses the fair value method to
account for all nonemployee stock-based compensation.
 
    (J)  COMPREHENSIVE INCOME (LOSS)
 
    TTI applies SFAS No. 130, REPORTING COMPREHENSIVE INCOME. The comprehensive
income (loss) for the years ended December 31, 1998, 1999 and 2000 does not
differ from the reported income (loss).
 
    (K)  FAIR VALUE OF FINANCIAL INSTRUMENTS
 
    The carrying amounts of TTI's financial instruments, which include cash
equivalents, accounts receivable, accounts payable, accrued expenses and
long-term obligations, approximate their fair value.
 
    (L)  USE OF ESTIMATES
 
    The preparation of financial statements in conformity with generally
accepted accounting principles requires management to make estimates and
assumptions that affect the reported amounts of assets and liabilities and
disclosure of contingent assets and liabilities at the date of the financial
statements and the reported amounts of revenues and expenses during the
reporting period. Actual results could differ from these estimates.
 
    (M)  NEW PRONOUNCEMENTS
 
    In June 1998, the Financial Accounting Standards Board (FASB) issued SFAS
No. 133, ACCOUNTING FOR DERIVATIVE INSTRUMENTS AND HEDGING ACTIVITIES, as
amended by SFAS No. 138, which establishes accounting and reporting standards
for derivative instruments, including certain derivative instruments embedded in
other contracts, and for hedging activities. It requires that an entity
recognize all derivatives as either assets or liabilities in the balance sheet
and measure those instruments at fair value. Pursuant to SFAS No. 137,
ACCOUNTING FOR DERIVATIVE INSTRUMENTS AND HEDGING ACTIVITIES--DEFERRAL OF THE
EFFECTIVE DATE OF SFAS NO. 133, SFAS No. 133 is effective in fiscal year 2001.
SFAS No. 133 is not expected to have a material impact on TTI's financial
condition or results of operations.
 
    In March 2000, the FASB issued Interpretation No. 44, ACCOUNTING FOR CERTAIN
TRANSACTIONS INVOLVING STOCK COMPENSATION--AN INTERPRETATION OF ACCOUNTING
PRINCIPLES BOARD OPINION NO. 25 (Interpretation No. 44). Interpretation No. 44
clarifies the application of APB Opinion No. 25, ACCOUNTING FOR STOCK ISSUED TO
EMPLOYEES. Interpretation No. 44 is effective July 1, 2000 but is retroactive
for certain events occurring after December 15, 1998. Interpretation No. 44 did
not have a material impact on TTI's consolidated financial condition or results
of operations.
 
                                      F-9

<PAGE>
                           TELECOM TECHNOLOGIES, INC.
 
             NOTES TO CONSOLIDATED FINANCIAL STATEMENTS (CONTINUED)
 
    (N)  NET INCOME (LOSS) PER SHARE
 
    Basic net income (loss) per share is computed by dividing net income (loss)
for the year by the weighted average number of common shares outstanding during
the year. Diluted net income (loss) per share is computed by dividing net income
(loss) for the year by the weighted average number of common shares and
potential common stock outstanding during the year, if dilutive. Basic and
diluted net income (loss) per share are the same, as any common stock to be
issued upon the exercise of stock options is to be contributed by the majority
stockholder and therefore is not dilutive (see Note 9(b)).
 
    (O)  DISCLOSURES ABOUT SEGMENTS OF AN ENTERPRISE
 
    SFAS No. 131, DISCLOSURES ABOUT SEGMENTS OF AN ENTERPRISE AND RELATED
INFORMATION, establishes standards for reporting information regarding operating
segments and related disclosures about products, services and geographic areas.
Operating segments are identified as components of an enterprise about which
separate discrete financial information is available for evaluation by the chief
operating decision maker, or decision making group, in making decisions
regarding resource allocation and assessing performance. To date, TTI has viewed
its operations and manages its business as principally one operating segment.
 
(2) ACQUISITION BY SONUS NETWORKS
 
    On January 18, 2001, Sonus acquired TTI. Upon the closing of this
acquisition, an aggregate of 10,800,000 shares of Sonus common stock (Merger
Shares) were exchanged for all outstanding shares of TTI common stock. Of the
Merger Shares, 1,200,000 shares were placed into escrow as security for TTI's
indemnity obligations under the merger agreement and will be released to TTI
stockholders upon expiration of those indemnity obligations, expected to be on
the first anniversary of the closing date. In addition to the Merger Shares, the
former TTI stockholders will have the right to receive up to an aggregate of
4,200,000 additional shares of Sonus common stock, which have been issued and
placed in escrow and will be released if certain specified business expansion
and product development milestones are achieved by TTI from time to time prior
to December 31, 2002. On June 6, 2001, 2,400,000 of the escrowed shares were
released to the former TTI stockholders upon achievement of specified
milestones. Sonus has also agreed to make contingent awards of up to 3,000,000
shares of common stock to certain employees of TTI who became employees of Sonus
as a result of the merger.
 
                                      F-10

<PAGE>
                           TELECOM TECHNOLOGIES, INC.
 
             NOTES TO CONSOLIDATED FINANCIAL STATEMENTS (CONTINUED)
 
(3) PROPERTY AND EQUIPMENT
 
    Property and equipment consist of the following, in thousands:
 

<TABLE>
<CAPTION>
                                                                ESTIMATED        DECEMBER 31,
                                                                 USEFUL       -------------------
                                                                  LIFE          1999       2000
                                                              -------------   --------   --------
<S>                                                           <C>             <C>        <C>
Equipment and software......................................     5 years      $ 2,350     $5,744
Furniture and fixtures......................................     7 years          113        113
Leasehold improvements......................................  Life of lease        91         91
                                                                              -------     ------
                                                                                2,554      5,948
Less accumulated depreciation and amortization..............                     (432)    (1,230)
                                                                              -------     ------
                                                                              $ 2,122     $4,718
                                                                              =======     ======
</TABLE>

 
    Included in property and equipment are $975,000 and $2,284,000 of equipment
purchased under capital lease obligations at December 31, 1999 and 2000,
respectively.
 
(4) BALANCE SHEET DATA
 
    (A)  ACCRUED EXPENSES
 
    Accrued expenses consist of the following, in thousands:
 

<TABLE>
<CAPTION>
                                                                 DECEMBER 31,
                                                              -------------------
                                                                1999       2000
                                                              --------   --------
<S>                                                           <C>        <C>
Employee compensation and related costs.....................   $1,168     $1,980
Accrued professional fees...................................       40      1,160
Accrued taxes...............................................      210        342
Other.......................................................      267        940
                                                               ------     ------
                                                               $1,685     $4,422
                                                               ======     ======
</TABLE>

 
    (B)  ALLOWANCE FOR DOUBTFUL ACCOUNTS
 
    The following is an analysis of TTI's allowance for doubtful accounts, in
thousands:
 

<TABLE>
<CAPTION>
                                                            CHARGED
                                               BALANCE,     TO COSTS                  BALANCE,
                                              BEGINNING       AND                      END OF
                                               OF YEAR      EXPENSES    DEDUCTIONS      YEAR
                                              ----------   ----------   -----------   ---------
<S>                                           <C>          <C>          <C>           <C>
  December 31, 1999.........................     $100         $ 73         $ (23)       $150
  December 31, 2000.........................      150          250            --         400
</TABLE>

 
(5) NOTE PAYABLE TO BANK
 
    TTI has a $10,000,000 demand line of credit with a bank, bearing interest at
the bank's prime rate (9.5% at December 31, 2000), available through March 31,
2001. The borrowings are based upon 80% of eligible accounts receivable
(Formula) and all of TTI's assets are pledged as collateral under the agreement.
Borrowings in excess of the Formula, up to $4,000,000, have been personally
 
                                      F-11

<PAGE>
                           TELECOM TECHNOLOGIES, INC.
 
             NOTES TO CONSOLIDATED FINANCIAL STATEMENTS (CONTINUED)
 
guaranteed by certain officers of TTI and the majority shareholder. At
December 31, 1999 and 2000, TTI had outstanding borrowings of $4,000,000 and
$7,000,000, respectively. At December 31, 2000, TTI had available borrowings
under the line of credit of $3,000,000, based upon the guarantee by certain
officers and the majority shareholder.
 
(6) INCOME TAXES
 
    The provision (benefit) for income taxes consist of the following, in
thousands:
 

<TABLE>
<CAPTION>
                                                                 YEAR ENDED
                                                                DECEMBER 31,
                                                             -------------------
                                                               1998       1999
                                                             --------   --------
<S>                                                          <C>        <C>
Current:
  Federal..................................................  $(1,960)    $ 144
  State....................................................     (277)       39
                                                             -------     -----
                                                              (2,237)      183
Deferred:
  Federal..................................................    2,087       134
  State....................................................      295        19
                                                             -------     -----
                                                               2,382       153
                                                             -------     -----
                                                             $  (145)    $ 336
                                                             =======     =====
</TABLE>

 
    TTI's effective tax rate differs from the statutory federal income tax rate
due to the following:
 

<TABLE>
<CAPTION>
                                                                   YEAR ENDED
                                                                  DECEMBER 31,
                                                             -----------------------
                                                               1998           1999
                                                             --------       --------
<S>                                                          <C>            <C>
Statutory federal rate.....................................    (34)%           34%
Research and development credit............................     --            (11)
Non-deductible expenses....................................      2              2
State income taxes, net of federal tax provision
  (benefit)................................................     (3)             3
                                                               ---            ---
  Effective tax rate.......................................    (35)%           28%
                                                               ===            ===
</TABLE>

 
    Deferred tax assets (liabilities) consist of the following, in thousands:
 

<TABLE>
<CAPTION>
                                                              DECEMBER 31,
                                                           -------------------
                                                             1999       2000
                                                           --------   --------
<S>                                                        <C>        <C>
Deferred tax assets (liabilities):
  Deferred revenue.......................................  $ 2,450    $ 4,072
  Net operating loss carryforwards.......................       --      1,047
  Tax credit carryforwards...............................       --        650
  Cash to accrual differences............................     (914)      (457)
  Depreciation...........................................      (34)       (69)
  Non-deductible reserves................................       37        148
  Other temporary differences............................      (74)       352
  Valuation allowance....................................   (1,066)    (5,344)
                                                           -------    -------
    Net deferred tax asset...............................  $   399    $   399
                                                           =======    =======
</TABLE>

 
                                      F-12

<PAGE>
                           TELECOM TECHNOLOGIES, INC.
 
             NOTES TO CONSOLIDATED FINANCIAL STATEMENTS (CONTINUED)
 
    TTI records a valuation allowance against its deferred tax assets to the
extent management believes it is more likely than not that the asset will not be
realized. At December 31, 2000, TTI had net deferred tax assets of approximately
$399,000, which will be realized through the utilization of available net
operating loss carrybacks.
 
    As of December 31, 2000, TTI had net operating loss carryforwards for income
tax purposes of approximately $2,829,000, which expire through 2020. TTI also
has available research and development credit carryforwards of approximately
$650,000 that expire through 2020. The Internal Revenue Code contains provisions
that limit the net operating loss and tax credit carryforwards available to be
used in any given year in the event of certain circumstances, including
significant changes in ownership interests. TTI has incurred an ownership change
upon the completion of the acquisition by Sonus which may have an impact on its
ability to use its net operating loss and tax carryforwards.
 
(7) COMMITMENTS
 
    TTI leases office space and certain equipment under various noncancelable
operating and capital leases. The capital leases are due in monthly installments
expiring at various dates through March 2005 and accrue interest at annual rates
ranging from 4.62% to 14.39%. TTI's future minimum annual payment obligations as
of December 31, 2000 under such leases are as follows, in thousands:
 

<TABLE>
<CAPTION>
                                                         OPERATING    CAPITAL
                                                         ----------   --------
<S>                                                      <C>          <C>
2001...................................................   $ 1,964      $  657
2002...................................................     3,232         640
2003...................................................     2,509         536
2004...................................................     2,418         195
2005...................................................     2,339          29
Thereafter.............................................     6,898          --
                                                          -------      ------
Total minimum lease payments...........................   $19,360       2,057
                                                          =======
Less amount representing interest......................                  (212)
                                                                       ------
Present value of minimum payments......................                 1,845
Less current portion...................................                  (553)
                                                                       ------
Long-term portion......................................                $1,292
                                                                       ======
</TABLE>

 
    Rent expense for all operating leases was approximately $596,000, $780,000
and $1,249,000 for the years ended December 31, 1998, 1999 and 2000,
respectively. Certain property and equipment has been pledged as security under
TTI's lease agreement for the corporate headquarters located in Richardson,
Texas.
 
                                      F-13

<PAGE>
                           TELECOM TECHNOLOGIES, INC.
 
             NOTES TO CONSOLIDATED FINANCIAL STATEMENTS (CONTINUED)
 
(8) REDEEMABLE COMMON STOCK
 
    During 1997, the majority stockholder of TTI sold 10% of the common stock of
TTI to an outside investor for $4,000,000. Under the terms of a stockholders'
agreement, the investor has a redemption option that became exercisable on
April 15, 2000. The redemption option allows the investor to require either the
majority stockholder or TTI to purchase all or any part of the shares held by
the investor at the then current fair market value as determined by an
independent appraiser. The redemption option terminates in the event TTI
receives an offer to purchase all of the outstanding common stock for at least
$100,000,000 which the majority stockholder elects to accept but which the
investor elects not to accept.
 
    In accordance with accounting principles generally accepted in the United
States, the carrying value of the redeemable common stock has been increased
based on changes in the fair market value of the common stock of TTI and has
been shown as a liability. Accordingly, during the years ended December 31,
1998, 1999 and 2000, TTI recorded a charge to accumulated deficit of $1,332,000,
$4,945,000 and $43,274,000, respectively, for the increase in the value of the
redeemable common stock. For purposes of these financial statements, the
estimated value of the redeemable common stock held by the investor of
$50,500,000 at December 31, 2000 is based upon the value of the TTI common stock
in the acquisition discussed in Note 2 using the closing sale price of Sonus
common stock on December 31, 2000. Upon consummation of the acquisition, the
redemption feature of this common stock terminated.
 
(9) STOCKHOLDERS' EQUITY
 
    (A)  COMMON STOCK
 
    On March 31, 1998, the Board of Directors approved an amendment to the
articles of incorporation that changed the common stock structure through an
exchange of all outstanding ordinary stock for Class A voting, no par and
Class B non-voting, no par, common stock. Through this amendment, the 1,000
common shares then outstanding were replaced with 3,888,889 Class A and
1,111,111 Class B shares.
 
    During 1999, TTI's Board of Directors approved an increase in the number of
authorized shares of common stock and two stock splits (which aggregated to a
20-for-1 split), increasing the number of issued and outstanding shares of
Class A common stock to 77,777,780 and increasing outstanding shares of Class B
common stock to 22,222,220. All common stock, stock options and per share
amounts in the accompanying consolidated financial statements and notes thereto
have been retroactively adjusted to reflect the stock splits.
 
                                      F-14

<PAGE>
                           TELECOM TECHNOLOGIES, INC.
 
             NOTES TO CONSOLIDATED FINANCIAL STATEMENTS (CONTINUED)
 
    (B)  EQUITY INCENTIVE PLAN
 
    On April 8, 1998, the Board of Directors adopted the telecom
technologies, inc. Equity Incentive Plan (the 1998 Plan). The 1998 Plan provides
for a maximum of 20,000,000 options for the purchase of Class B non-voting
common stock to be granted to employees and consultants with exercise prices
equal to the fair market value of the stock as of the date of grant. Under the
1998 Plan, TTI may grant incentive or non-qualified stock options. The options
generally vest ratably over a period of two to four years and expire after five
years.
 
    A summary of activity under the 1998 Plan is as follows:
 

<TABLE>
<CAPTION>
                                                                                      WEIGHTED
                                                                                      AVERAGE
                                                            NUMBER OF     EXERCISE    EXERCISE
                                                              SHARES       PRICE       PRICE
                                                            ----------   ----------   --------
<S>                                                         <C>          <C>          <C>
Outstanding, December 31, 1997............................          --   $       --    $  --
  Granted.................................................   3,300,000         0.80     0.80
  Canceled................................................    (320,000)        0.80     0.80
                                                            ----------
Outstanding, December 31, 1998............................   2,980,000         0.80     0.80
  Granted.................................................   9,919,800    0.80-1.00     0.91
  Canceled................................................    (220,000)   0.80-1.00     0.80
                                                            ----------
Outstanding, December 31, 1999............................  12,679,800    0.80-1.00     0.89
  Granted.................................................   4,121,270    1.00-2.00     1.22
  Canceled................................................    (423,905)        0.80     0.80
  Exercised...............................................    (361,670)        0.80     0.80
                                                            ----------
Outstanding, December 31, 2000............................  16,015,495   $0.80-2.00    $0.97
                                                            ==========   ==========    =====
Exercisable, December 31, 2000............................   3,790,694   $0.80-1.00    $0.87
                                                            ==========   ==========    =====
</TABLE>

 
    The fair value weighted average per share of options granted during the
years ended December 31, 1998, 1999 and 2000 was $0.35, $0.40 and $0.54,
respectively. The grant date fair values were estimated using the Black-Scholes
option pricing model. The weighted average remaining life of the options
outstanding at December 31, 2000 was approximately 3.7 years.
 
    During 1997, the majority stockholder of TTI sold 10% of her then 100%
ownership of the common stock of TTI to an outside investor. In connection with
the sale, TTI, the majority stockholder and the investor agreed that the
investor would not be diluted below 10% ownership of TTI from the issuance of
additional equity in TTI, including stock options.
 
    In order to prevent the exercise of options under the 1998 Plan from
diluting the investor below 10% ownership, the majority stockholder agreed to
fund option exercises from her personal holdings of class B non-voting common
stock. Accordingly, as stock options are exercised, the proceeds are collected
by TTI and remitted to the majority stockholder, who in turn transfers the
number of shares for which the option has been exercised to TTI for delivery to
the option holder. TTI acts only as a facilitator for the transfer of stock from
its majority stockholder to its option holders upon the exercise of options. No
new equity is issued by TTI as the result of any option exercises.
 
                                      F-15

<PAGE>
                           TELECOM TECHNOLOGIES, INC.
 
             NOTES TO CONSOLIDATED FINANCIAL STATEMENTS (CONTINUED)
 
    (C)  STOCK-BASED COMPENSATION
 
    Stock-based compensation expenses includes the amortization of deferred
employee compensation and other equity related expenses for non-employees.
 
    In connection with certain employee stock option grants for the year ended
December 31, 2000, TTI recorded deferred compensation of $10,263,000. This
represents the aggregate difference between the exercise price and the fair
value of the common stock on the date of grant for accounting purposes. The
deferred compensation will be recognized as an expense over the vesting period
of the underlying stock options. TTI recorded compensation expense of $1,216,000
for the year ended December 31, 2000, related to these options. Based on the
grant of these stock options, TTI expects to record approximately $4,761,000,
$2,488,000, $1,302,000 and $496,000 in employee compensation expense for the
years ending December 31, 2001, 2002, 2003 and 2004, respectively.
 
    TTI has valued the stock options granted to non-employees based upon the
Black-Scholes option pricing model. As of December 31, 1999 and 2000, TTI had
25,000 and 575,000 stock options, respectively, outstanding to non-employees.
Stock-based compensation expense for the grant of options to non-employees was
not material for the year ended December 31, 1999. TTI has recorded stock-based
compensation expense of $731,000 for the grant of options to non-employees for
the year ended December 31, 2000. In accordance with Emerging Issues Task Force
96-18, TTI will record the value as the services are provided.
 
    TTI has computed the pro forma disclosures required under SFAS No. 123 for
options granted to employees for the years ended December 31, 1998, 1999 and
2000, using the Black-Scholes option pricing model with an assumed risk-free
interest rate of 5.0%, 60% volatility and an expected life of 3 years with the
assumption that no dividends will be paid. Had compensation expense been
determined consistent with SFAS No. 123, the pro forma net income (loss) and pro
forma net income (loss) per share would have been as follows:
 

<TABLE>
<CAPTION>
                                                                        YEAR ENDED
                                                                       DECEMBER 31,
                                                              ------------------------------
                                                                1998       1999       2000
                                                              --------   --------   --------
<S>                                                           <C>        <C>        <C>
Net income (loss), in thousands--
  As reported...............................................   $ (265)    $ 867     $(11,454)
  Pro forma.................................................   $ (436)    $ 372     $(12,454)
Basic and diluted net income (loss) per share--
  As reported...............................................   $(0.00)    $0.01     $  (0.11)
  Pro forma.................................................   $(0.00)    $0.00     $  (0.12)
</TABLE>

 
(10)  RELATED-PARTY TRANSACTION
 
    In June 1999, TTI issued a demand note receivable to its majority
stockholder for $1,486,000. This note accrued interest at 9.75% annually and was
repaid in full in November 1999.
 
                                      F-16

<PAGE>
                           TELECOM TECHNOLOGIES, INC.
 
             NOTES TO CONSOLIDATED FINANCIAL STATEMENTS (CONTINUED)
 
(11)  401(K) PLAN
 
    TTI sponsors a defined contribution pension plan covering substantially all
employees. TTI's contributions to this plan are based on percentages of
participants' wages. During the years ended December 31, 1998, 1999 and 2000,
TTI made contributions totaling approximately $29,000, $210,000 and $280,000,
respectively.
 
(12)  ACQUISITIONS AND DISPOSITIONS
 
    (A)  PURCHASE OF SEQUEL SYSTEMS
 
    On August 31, 1999, TTI purchased substantially all of the assets of Sequel
Systems, Inc. (Sequel) for cash of $889,000 and a software license valued at
$150,000. Additional direct cash costs of the acquisition totaled approximately
$15,000. Sequel provided professional services related to data conversion, data
migration and circuit design in connection with telecommunication systems
software industry specializing in open computing technology solutions and
methodology. The transaction was accounted for under the purchase method of
accounting, whereby the assets and liabilities of Sequel were recorded by TTI at
their fair value at the time of acquisition. In connection with the acquisition,
TTI recorded accounts receivable and property and equipment of $828,000 and
$226,000, respectively. The Sequel results of operations have been included in
TTI's consolidated financial statements beginning with the date of acquisition.
 
    (B)  SALE OF PRODUCT LINE
 
    In December 1998, TTI entered into an agreement to sell the assets related
to its network testing software product line for $5,500,000. As part of the
agreement, the purchaser agreed to purchase, at fair market value, research and
development and manufacturing services from TTI for a minimum of two years.
These service agreements were not renewed upon the expiration of the initial
term in January 2001. TTI has also agreed to provide consulting and support
services for end users on a time and materials basis. In addition, the purchaser
has agreed to pay royalties on future sales of the product line.
 
    The revenue from this transaction was recorded in 1999, as the sale was
contingent upon the execution of the research and development and manufacturing
agreements, which were signed on January 11, 1999. These future services are not
essential to the functionality of the assets being sold and have been contracted
at their fair value.
 
    The proceeds from the sale of this product line are presented in other
income in the accompanying consolidated statements of operations. Employees and
certain assets associated with the network testing software product line were
retained by TTI for the purposes of fulfilling TTI's obligations under the
research and development and contract manufacturing agreements. For the years
ended December 31, 1999 and 2000, revenues under these agreements included in
product revenues in the accompanying consolidated statements of operations
totaled $7,372,000 and $7,033,000, respectively.
 
(13)  INSURANCE SETTLEMENT
 
    In April 1999, TTI received a settlement of approximately $620,000 under the
terms of a business interruption insurance policy applicable to a prior-year
claim. This amount has been included in other income in the accompanying
consolidated statements of operations. Approximately $420,000 and $100,000 was
paid to TTI during 1999 and 2000, respectively, with the remaining $100,000 to
be paid during 2001.
 
                                      F-17





<PAGE>
                                                                    EXHIBIT 99.2
 
          UNAUDITED PRO FORMA CONDENSED COMBINED FINANCIAL INFORMATION
 
    The following unaudited pro forma condensed combined financial information
gives effect to the acquisition of TTI by Sonus using the purchase method of
accounting after giving effect to the pro forma adjustments described in the
accompanying notes. The unaudited pro forma condensed combined financial
information should be read in conjunction with the audited historical
consolidated financial statements and related notes of Sonus and TTI.
 
    Pursuant to the terms of the merger agreement, a wholly owned subsidiary of
Sonus merged into TTI and the stockholders of TTI were entitled to receive up to
an aggregate of 15,000,000 shares of Sonus common stock. Of these shares,
9,600,000 were issued to the TTI stockholders on January 18, 2001 and an
aggregate of up to 1,200,000 escrowed shares may be released to Sonus in
satisfaction of indemnification claims that may be made by Sonus under the
merger agreement. The remaining 4,200,000 shares are held in escrow for release
to the former TTI stockholders if certain agreed upon specified business
expansion and product development performance milestones are achieved by TTI

from time to time prior to December 31, 2002.
 
    Sonus has issued contingent awards of 3,000,000 shares of common stock to
certain employees of TTI who became employees of Sonus as a result of the merger
under the 2000 Retention Plan. These awards will vest in equal installments on
each of October 31, 2002, November 30, 2002, January 31, 2003 and February 28,
2003, if (1) the recipients do not voluntarily terminate employment with TTI or
Sonus prior to such vesting dates, and (2) the business expansion and product
development escrow release conditions are satisfied in whole or in part. The
portion of the total number of shares of Sonus common stock awarded to each
employee that will be deemed vested on each vesting date will not exceed the
proportion of all of the shares escrowed in the merger subject to the
satisfaction of the business expansion and product development escrow release
conditions that have been released prior to such vesting date. Generally, any
awards forfeited by employees who terminate employment with TTI, other than a
termination by Sonus or TTI without cause, prior to the date on which they would
otherwise vest, may be reallocated to remaining TTI employees, awarded to
replacement hires or returned to Sonus as provided by the terms of this plan.
The value of the 3,000,000 shares awarded under the retention plan is being
expensed ratably over the approximate two-year vesting period based upon the
closing price of Sonus common stock on the date the merger was consummated, as
adjusted for the change in the fair value of Sonus common stock on the date the
specific escrow release conditions are satisfied.
 
    The acquisition was accounted for using the purchase method of accounting in
accordance with Accounting Principles Board (APB) No. 16. Accordingly, the total
purchase price has been allocated to the assets acquired and liabilities assumed
based upon their estimated fair values. The purchase price has been determined
by using the average market value of Sonus common stock for the period from two
days before to two days after the announcement of the TTI merger ($41.61 per
share) to value the 10,800,000 Sonus common shares deemed to be issued to the
TTI shareholders at the closing date, comprised of the 9,600,000 shares issued
on January 18, 2001 and the 1,200,000 indemnity escrowed shares, and the fair
value of the portion of the 4,200,000 escrow shares earned for accounting
purposes, the fair value of liabilities assumed and expenses of the merger. The
purchase price which has been used for the unaudited pro forma condensed
combined financial information is as follows, in thousands:
 

<TABLE>
<CAPTION>
 
<S>                                                           <C>
Fair market value of shares issued..........................  $498,619
Liabilities assumed.........................................    21,184
Acquisition expenses........................................     6,327
                                                              --------
                                                              $526,130
                                                              ========
</TABLE>

 
                                      F-1

<PAGE>
    UNAUDITED PRO FORMA CONDENSED COMBINED FINANCIAL INFORMATION (CONTINUED)
 
    With the assistance of valuation experts, the purchase price has been
allocated to the tangible and intangible assets acquired based upon their fair
values. Based upon these appraisals, the purchase price allocation is as
follows, in thousands:
 

<TABLE>
<CAPTION>
 
<S>                                                           <C>
Tangible assets.............................................  $  6,312
Intangible assets:
  Workforce, developed technology and customer list.........    32,300
  In-process research and development.......................    40,000
  Deferred compensation related to unvested options.........    22,600
  Goodwill..................................................   424,918
                                                              --------
                                                              $526,130
                                                              ========
</TABLE>

 
    To the extent that any of the 4,200,000 escrowed shares are earned for
accounting purposes, the purchase price and goodwill will be adjusted by the
value of such shares on the date the relevant escrow release condition is
satisfied.
 
    Sonus engaged third-party appraisers to conduct a valuation of the
intangible assets and to assist in the determination of useful lives for such
assets. Based on the appraisal, $40,000,000 has been allocated to in-process
research and development which was expensed in the first quarter of 2001. The
amounts allocated to developed technology, customer list, assembled workforce
and goodwill is being amortized over their estimated useful lives of 3 years.
Deferred compensation was computed based on the value for accounting purposes of
the unvested TTI options assumed by Sonus and will be expensed over the
remaining vesting period of up to 4 years.
 
    The valuation of in-process research and development was determined using
the income method. Revenue and expense projections for the in-process
development project were prepared by the management of Sonus through 2008 and
the present value was computed using a discount rate of 22.5%. The in-process
project is not expected to reach technological feasibility until the end of
2001, at an estimated cost to complete of approximately $5,000,000. In the event
that the project is not completed and technological feasibility is not achieved,
there is no alternative future use for the in-process technology. The
assumptions used for the valuation of in-process research and development are
the responsibility of management and are subject to change.
 
    The unaudited pro forma condensed combined financial information does not
purport to represent what the consolidated results of operations actually will
be at the beginning of the periods presented or to project the results of
operations for any future period or at a future date. For example, over our next
several quarters the sources from which TTI has historically derived revenue are
expected to decline significantly as we accelerate our shift in focus to the
development and deployment of the INtelligentIP softswitch product. In addition,
as a result of TTI's sale of its network testing software product line, revenues
related to these products will decline or cease in 2001. The unaudited pro forma
financial information does not give effect to any cost savings and other
synergies that may result from the merger. Sonus is developing plans for
integration of TTI and has not determined if there will be any cost savings.
 
                                      F-2

<PAGE>
                         UNAUDITED PRO FORMA CONDENSED
                        COMBINED STATEMENT OF OPERATIONS
 
                      FOR THE YEAR ENDED DECEMBER 31, 2000
 
                     (IN THOUSANDS, EXCEPT PER SHARE DATA)
 

<TABLE>
<CAPTION>
                                                     HISTORICAL
                                                --------------------    PRO FORMA       PRO FORMA
                                                 SONUS        TTI      ADJUSTMENTS      COMBINED
                                                --------   ---------   -----------      ---------
<S>                                             <C>        <C>         <C>              <C>
REVENUES......................................  $ 51,770   $  28,631    $      --       $  80,401
Manufacturing, product and service costs......    27,848      14,381           --          42,229
                                                --------   ---------    ---------       ---------
GROSS PROFIT..................................    23,922      14,250           --          38,172
 
OPERATING EXPENSES:
  Research and development....................    26,430      14,735           --          41,165
  Sales and marketing.........................    21,569       5,090           --          26,659
  General and administrative..................     5,477       3,586           --           9,063
  Amortization of intangibles.................        --          --      148,354(A)      148,354
  Stock-based compensation....................    26,729       1,947       50,489(B)       79,165
                                                --------   ---------    ---------       ---------
      Total operating expenses................    80,205      25,358      198,843         304,406
                                                --------   ---------    ---------       ---------
LOSS FROM OPERATIONS..........................   (56,283)    (11,108)    (198,843)       (266,234)
Other income (expense), net...................     6,245        (346)          --           5,899
                                                --------   ---------    ---------       ---------
NET LOSS......................................  $(50,038)  $ (11,454)   $(198,843)      $(260,335)
                                                ========   =========    =========       =========
NET LOSS PER SHARE:
  Basic and diluted...........................  $  (0.52)  $   (0.11)                   $   (2.44)
                                                ========   =========                    =========
  Pro forma basic and diluted.................  $  (0.37)  $   (0.11)                   $   (1.78)
                                                ========   =========                    =========
SHARES USED IN COMPUTING NET LOSS PER SHARE:
  Basic and diluted...........................    95,877     100,000       10,800         106,677
                                                ========   =========    =========       =========
  Pro forma basic and diluted.................   135,057     100,000       10,800         145,857
                                                ========   =========    =========       =========
</TABLE>

 
   SEE NOTES TO UNAUDITED PRO FORMA CONDENSED COMBINED FINANCIAL INFORMATION.
 
                                      F-3

<PAGE>
                         UNAUDITED PRO FORMA CONDENSED
                        COMBINED STATEMENT OF OPERATIONS
 
                   FOR THE THREE MONTHS ENDED MARCH 31, 2001
 
                     (IN THOUSANDS, EXCEPT PER SHARE DATA)
 

<TABLE>
<CAPTION>
                                                   HISTORICAL
                                        ---------------------------------
                                         THREE MONTHS
                                            ENDED         18 DAYS ENDED
                                        MARCH 31, 2001   JANUARY 18, 2001
                                        --------------   ----------------    PRO FORMA       PRO FORMA
                                            SONUS              TTI          ADJUSTMENTS      COMBINED
                                        --------------   ----------------   -----------      ---------
<S>                                     <C>              <C>                <C>              <C>
REVENUES..............................     $  41,499         $     335      $       --       $  41,834
Manufacturing, product and service
  costs...............................        18,011               124              --          18,135
                                           ---------         ---------      ----------       ---------
GROSS PROFIT..........................        23,488               211              --          23,699
 
OPERATING EXPENSES:
  Research and development............        13,919             1,155              --          15,074
  Sales and marketing.................         8,488               152              --           8,640
  General and administrative..........         2,663             2,182          (2,008)(D)       2,837
  Stock-based compensation............        15,423                96           2,419 (B)      17,938
  Amortization of intangibles.........        27,207                --           6,802 (A)      34,009
  In-process research and
    development.......................        40,000                --         (40,000)(C)          --
                                           ---------         ---------      ----------       ---------
      Total operating expenses........       107,700             3,585         (32,787)         78,498
                                           ---------         ---------      ----------       ---------
LOSS FROM OPERATIONS..................       (84,212)           (3,374)         32,787         (54,799)
Other income (expense)................         1,733                 3              --           1,736
                                           ---------         ---------      ----------       ---------
NET LOSS..............................     $ (82,479)        $  (3,371)     $   32,787       $ (53,063)
                                           =========         =========      ==========       =========
PER SHARE INFORMATION:
  Basic and diluted net loss per
    share.............................     $   (0.51)        $   (0.03)                      $   (0.32)
                                           =========         =========                       =========
  Shares used in computation..........       162,091           100,000           2,160         164,251
                                           =========         =========      ==========       =========
</TABLE>

 
   SEE NOTES TO UNAUDITED PRO FORMA CONDENSED COMBINED FINANCIAL INFORMATION.
 
                                      F-4

<PAGE>
     NOTES TO UNAUDITED PRO FORMA CONDENSED COMBINED FINANCIAL INFORMATION
 
BASIS OF PRESENTATION
 
    The unaudited pro forma condensed combined statements of operations for the
year ended December 31, 2000 and the three months ended March 31, 2001 give
effect to the acquisition as if the transaction had occurred at the beginning of
each period presented.
 
    Below is a table of the purchase price allocation, which reflects the total
purchase price of $526,130,000, consisting of the 10,800,000 shares of Sonus
common stock issued on January 18, 2001, composed of the 9,600,000 shares and
the 1,200,000 indemnity escrow shares, which have been valued at $450,000,000,
the fair value of the portion of the 4,200,000 escrow shares earned for
accounting purposes as of March 31, 2001 of $48,619,000, acquisition related
fees and expenses of $6,327,000 and assumed liabilities of $21,184,000, in
thousands:
 

<TABLE>
<CAPTION>
 
<S>                                                           <C>
Tangible assets acquired....................................  $  6,312
Intangible assets acquired:
  Workforce, developed technology and customer list.........    32,300
  In-process research and development.......................    40,000
  Deferred compensation related to unvested options.........    22,600
  Goodwill..................................................   424,918
                                                              --------
                                                              $526,130
                                                              ========
</TABLE>

 
PRO FORMA ADJUSTMENTS
 
    Adjustments to record amortization of intangibles in the unaudited pro forma
condensed combined statements of operations, in thousands:
 

<TABLE>
<CAPTION>
                                                                                                             THREE
                                                                                            YEAR ENDED    MONTHS ENDED
                                                                              ESTIMATED    DECEMBER 31,    MARCH 31,
                                                                             USEFUL LIFE       2000           2001
                                                                             -----------   ------------   ------------
       <S>                    <C>                                            <C>           <C>            <C>
       (A)                    Amortization of intangibles:
                              Workforce, developed
                              technology and customer list.................    3 years       $ 10,767       $    539
                              Goodwill.....................................    3 years        137,587          6,263
                                                                                             --------       --------
                                                                                             $148,354       $  6,802
                                                                                             ========       ========
</TABLE>

 
                                      F-5

<PAGE>
     NOTES TO UNAUDITED PRO FORMA CONDENSED COMBINED FINANCIAL INFORMATION
                                  (CONTINUED)
 
PRO FORMA ADJUSTMENTS (CONTINUED)
 

<TABLE>
<CAPTION>
                                                                                                              THREE MONTHS
                                                                                            YEAR ENDED            ENDED
                                                                                           DECEMBER 31,         MARCH 31,
                                                                                               2000               2001
                                                                                         ----------------   -----------------
                                                                                                    (IN THOUSANDS)
       <S>                    <C>                                            <C>         <C>                <C>
       (B)                    Stock based compensation:
 
                              To record stock-based compensation related to 3,000,000        $ 37,563           $  2,194
                              shares of Sonus common stock awarded under the 2000
                              Retention Plan. These shares vest in equal installments
                              on each of October 31, 2002, November 30, 2002,
                              January 31, 2003 and February 28, 2003, if the
                              recipients maintain employment through each of such
                              dates, and if TTI achieves certain business expansion
                              and product development milestones.
 
                              To record amortization of deferred compensation related
                              to unvested options.....................................         12,926                225
                                                                                             --------           --------
                              Total...................................................       $ 50,489           $  2,419
                                                                                             ========           ========
 
       (C)                    To reverse in-process research and development charge...       $     --           $(40,000)
                                                                                             ========           ========
 
       (D)                    To reverse TTI's acquisition related expenses...........       $     --           $ (2,008)
                                                                                             ========           ========
</TABLE>

 
NET LOSS PER SHARE
 
   The unaudited basic and diluted net loss per share is based on the weighted
average number of Sonus unrestricted common shares outstanding prior to the
acquisition plus the 10,800,000 shares of Sonus common stock issued upon the
closing of the acquisition. The unaudited pro forma basic and diluted net loss
per share reflects the conversion of all outstanding shares of Sonus Series A,
B, C and D redeemable convertible preferred stock into an aggregate of
96,957,222 shares of common stock upon the consummation of the Sonus IPO in May
2000, as if such conversion occurred at the date of original issuance. Options
outstanding and the shares to be issued under the 2000 Retention Plan have not
been included in the computation of the basic and diluted net loss per share for
the periods reported because their effect would not be dilutive.
 
                                      F-6



<PAGE>
                                                                    EXHIBIT 99.3
 
                            CERTIFICATE OF AMENDMENT
                                       OF
            FOURTH AMENDED AND RESTATED CERTIFICATE OF INCORPORATION
                                       OF
                              SONUS NETWORKS, INC.
 
    Sonus Networks, Inc., a corporation organized and existing under and by
virtue of the General Corporation Law of the State of Delaware (the
"CORPORATION"), DOES HEREBY CERTIFY:
 
    FIRST: That at a meeting of the Board of Directors of the Corporation,
resolutions were duly adopted setting forth a proposed amendment to the Fourth
Amended and Restated Certificate of Incorporation of said corporation, declaring
said amendment to be advisable and directing the holders of Common Stock of said
corporation to consider said amendment and to indicate their approval and
adoption thereof. The resolution setting forth the proposed amendment is as
follows:
 
    RESOLVED:  That the first sentence of Article IV of the Fourth Amended and
               Restated Certificate of Incorporation of the Corporation be, and
               it hereby is, amended to read as follows:
 
           The total number of shares of capital stock which the
           corporation shall have authority to issue is 605,000,000,
           consisting solely of:
 
               600,000,000 shares of common stock, par value
               $0.001 per share ("Common Stock"); and
 
               5,000,000 shares of preferred stock, par value
               $0.01 per
 share ("Preferred Stock").
 
    RESOLVED:  That except as expressly amended hereby no other aspect of such
               Article IV shall be modified hereby.
 
    SECOND: That thereafter, pursuant to said resolutions of its Board of
Directors, the holders of record of not less than a majority of the issued and
outstanding shares of Common Stock of said Corporation, representing not less
than the minimum number of votes necessary to authorize and take such action,
duly adopted such an amendment at the Annual Meeting of the Shareholders in
accordance with Sections 211 and 222 of the General Corporation Law of the State
of Delaware.
 
    THIRD: That said amendment was duly adopted in accordance with the
provisions of Section 242 of the General Corporation Law of the State of
Delaware.
 
    IN WITNESS WHEREOF, the Corporation has caused this certificate to be signed
by Stephen J. Nill, its Vice President Finance and Administration and Chief
Financial Officer, this 29th day of May, 2001.
 

<TABLE>
<S>                                                    <C>  <C>
                                                       SONUS NETWORKS, INC.
 
                                                       By:  /s/ STEPHEN J. NILL
                                                            -----------------------------------------
                                                            Stephen J. Nill
                                                            VICE PRESIDENT FINANCE AND ADMINISTRATION
                                                            AND CHIEF FINANCIAL OFFICER
</TABLE>