UNITED STATES

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

February 20, 2009

Date of Report (Date of earliest event reported)

SONUS NETWORKS, INC.

(Exact Name of Registrant as Specified in its Charter)

7 TECHNOLOGY PARK DRIVE, WESTFORD, MASSACHUSETTS 01886

(Address of Principal Executive Offices) (Zip Code)

(978) 614-8100

(Registrant’s telephone number, including area code)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions (see General Instruction A.2. below):

¨  Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425)

¨  Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12)

¨  Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b))

¨  Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))

Item 5.02. Departure of Directors or Certain Officers; Election of Directors; Appointment of Certain Officers; Compensatory Arrangements of Certain Officers.

On February 20, 2009, the Registrant’s Board of Directors (the “Board”) appointed Scott E. Schubert as a director to fill a vacancy on its Board.  Mr. Schubert will serve until the 2009 Annual Meeting of Stockholders or until his successor is duly appointed and qualified.

From August 2005 to December 2008, Mr. Schubert served as the Chief Financial Officer of Transunion, LLC.  From February 2003 to May 2005, Mr. Schubert served as Chief Financial Officer of NTL Inc. (now Virgin Media, Inc.), where he had also held the position of Executive Vice President of Corporate Development.

Mr. Schubert was recommended to the Board by the Nominating Committee of the Board in accordance with the provisions of the Nominating Committee Charter.  Mr. Schubert has been appointed to serve on the Audit Committee of the Board.  There are no arrangements or understandings between Mr. Schubert and any other person pursuant to which Mr. Schubert was elected as a director.  There are no transactions in which Mr. Schubert has an interest requiring disclosure under Item 404(a) of Regulation S-K.

Mr. Schubert will be granted a stock option, pursuant to the Registrant’s 2007 Stock Incentive Plan, to purchase 50,000 shares of the Registrant’s common stock with an exercise price equal to the closing share price of the Registrant’s common stock on the date of grant, March 15, 2009.  Such option will vest over a four-year period so long as Mr. Schubert remains a member of the Board.

A copy of the press release announcing Mr. Schubert’s appointment is filed as Exhibit 99.1 hereto.

Item 9.01. Financial Statements and Exhibits.

(d)           Exhibits

99.1                           Press release of Sonus Networks, Inc. dated February 23, 2009 announcing the appointment of a new director to the Board of Directors.

2

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.

3

Exhibit Index

99.1                           Press release of Sonus Networks, Inc. dated February 23, 2009 announcing the appointment of a new director to the Board of Directors.

4

Exhibit 99.1

FOR IMMEDIATE RELEASE

SONUS NETWORKS APPOINTS SCOTT E. SCHUBERT TO BOARD OF DIRECTORS

Former Executive Vice President and Chief Financial Officer of TransUnion LLC

Further Strengthens Board Of Leading Provider Of IP-Voice Technology

Westford, MA, February, 23, 2009 - Sonus Networks, Inc. (Nasdaq: SONS), a market leader in IP communications infrastructure, today announced that Scott E. Schubert has been appointed to its Board of Directors and will serve as a member of the Sonus Audit Committee.  With a career in senior finance roles spanning over 30 years, Mr. Schubert complements the expertise of the current Board and brings further depth of knowledge to the Company’s strategic leadership.

Mr. Schubert retired from TransUnion LLC in December 2008, having served as chief financial officer for three years.  Mr. Schubert joined TransUnion from NTL Inc. (now Virgin Media, Inc.), where he had served as executive vice president of Corporate Development and had been its chief financial officer since 2003.  Prior to NTL Inc., Mr. Schubert held the position of chief financial officer at WilTel/Williams Communications from 1999 to 2003, and prior to that served as head of BP Amoco’s Global Financial Services, leading the initial integration of BP and Amoco’s worldwide financial operations following the merger of those two companies.

“Strong financial leadership is important to Sonus,” commented Howard Janzen, chairman of the board at Sonus Networks.  “Having known Scott for a number of years, I know he shares the Sonus commitment to profitable growth and building long-term shareholder value. We look forward to working with him.”

Mr. Schubert is a graduate of the Krannert School of Business at Purdue University, where he completed his MBA degree in Finance and Economics in 1976.  He also earned his Bachelor of Science degree at Purdue in 1975, with dual majors in Engineering and Accounting.

This appointment fills the open seat left by Edward T. Anderson, who announced his retirement from the Sonus Board of Directors in December 2008.

About Sonus Networks

Sonus Networks, Inc. is a market leader in IP communications infrastructure for wireline and wireless service providers.  With its comprehensive IP Multimedia Subsystem (IMS) solution, Sonus addresses the full range of carrier applications, including residential and business voice services, wireless voice and multimedia, trunking and tandem switching, carrier interconnection and enhanced services.  Sonus’ voice infrastructure solutions are deployed in service provider networks worldwide.  Founded in 1997, Sonus is headquartered in Westford, Massachusetts.  Additional information on Sonus is available at http://www.sonusnet.com.

This release may contain forward-looking statements regarding future events that involve risks and uncertainties. Readers are cautioned that these forward-looking statements are only predictions and may differ materially from actual future events or results.  Readers are referred to Item 1A “Risk Factors” of our Annual Report on Form 10-K for the year ended December 31, 2007 and all subsequent Quarterly Reports on Form 10-Q, which identify important risk factors that could cause actual results to differ from those contained in the forward-looking statements.  Risk factors include among others: the Company’s ability to align its cost structure with market conditions, the impact of material weaknesses in our disclosure controls and procedures and our internal control over financial reporting on our ability to report our financial results timely and accurately; the unpredictability of our quarterly financial results; risks and uncertainties associated with the Company’s restatement of its historical stock option granting practices and accounting including regulatory actions; actions that may be taken by significant shareholders; risks associated with our international expansion; and the impact the current global financial market conditions may have on the telecommunications industry.  Any forward-looking statements represent Sonus’ views only as of today and should not be relied upon as representing Sonus’ views as of any subsequent date.  While Sonus may elect to update forward-looking statements at some point, Sonus specifically disclaims any obligation to do so, except as required by law.

Sonus is a registered trademark of Sonus Networks, Inc. All other company and product names may be trademarks of the respective companies with which they are associated.