Industry Leading Provider of IMS-Ready Solutions Adds New Certification Program to Help Drive Adoption of SIP-Based Next Generation Communications Services

CHELMSFORD, Mass., September 12, 2006 – Sonus Networks, Inc. (Nasdaq: SONS), a leading supplier of service provider Voice over IP (VoIP) infrastructure solutions, announced today that as part of its Open Services Partner Alliance (OSPA), the industry's largest interoperability and testing program, the Company has added a new Interoperability Certification Program to streamline the delivery of Session Initiation Protocol (SIP)-based products and services into the rapidly evolving IP-based voice market. The new certification program, which will leverage the University of New Hampshire InterOperability Lab (UNH-IOL) to conduct extensive testing, is in response to the increasing demand for interoperability certification with Sonus' industry leading platform.

"As Sonus-based networks continue to become more pervasive on a global scale, there's a mandate from network operators and equipment vendors alike to leverage Sonus' extensive field experience to verify the interoperability capabilities of many different pieces of the network," said Steve Edwards, chief marketing officer, Sonus Networks. "Sonus has always been a leader in the industry in this regard, and the new Certification Program enhances our ability to respond to our customer needs and help them build robust, unique networks."

The OSPA program has been an invaluable ingredient in helping Sonus customers to integrate products from multiple vendors into their Sonus-based IP Multimedia Subsystem (IMS)-ready network. The OSPA supports two levels of partnerships: strategic partnerships, whereby partner products are integrated with the Sonus IMS-ready architecture to promote rapid, reliable deployments; and, technology partnerships, which are designed to test the SIP capabilities and interoperability of products that address a specific carrier need or technology niche. The new OSPA Interoperability Certification Program will increase Sonus' ability to certify a wider variety of products and services, increasing the value proposition for Sonus customers worldwide by helping them to stay ahead of the innovation curve.

"Interoperability becomes increasingly important as the telecom industry moves aggressively toward standards-based networks," said Joe McGarvey, Principal Analyst, Current Analysis. "Sonus, a pioneer in the use of SIP and a driving force in the IMS movement, has a strong presence in many of the world's leading IP-based voice networks. An interoperability testing program of this size and scale is valuable to network operators as it helps ensure that the different pieces of these highly sophisticated networks work seamlessly together."

By working with the UNH InterOperability Lab, Sonus will streamline the costs and time resources associated with the testing process. The UNH-IOL's 32,000 square foot data-communications testing lab is one of the best-equipped and most well-established testing facilities. The lab offers extensive testing services backed by thorough knowledge of leading industry standards and more than $20 million in test bed and test equipment gear.

"Sonus is at the forefront of an industry that is evolving very quickly, and we hope that by working in conjunction with our testing program, Sonus can help network operators move even faster in the pursuit of next generation voice networks," said Tim Winters, UNH-IOL Senior Engineer.

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About Sonus Networks

Sonus Networks, Inc. is a leading provider of voice over IP (VoIP) infrastructure solutions 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 Chelmsford, 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 the “Risk Factors" section of Sonus' Quarterly Report on Form 10-Q, dated May 8, 2006, filed with the Securities and Exchange Commission, which identifies important risk factors that could cause actual results to differ from those contained in the forward-looking statements. Risk factors include among others: 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 announced review of its historical stock option grants and accounting, including any potential impact of the Company's financial statements or results, the Company's inability to timely report with the Securities and Exchange Commission, the Company's potential inability to meet NASDAQ requirements for continued listing, potential investigations or litigation arising out of the review or any restatement; risks associated with our international expansion and growth; consolidation in the telecommunications industry; and potential costs resulting from pending securities litigation against the company. 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.

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