Industry Leaders Team to Drive IMS Interoperability

WESTFORD, Mass., November 20, 2007 – Sonus Networks, Inc. (Nasdaq: SONS), a leading supplier of service provider IP-voice infrastructure solutions, announced today that it has successfully completed a battery of tests designed to validate the Company's IP Multimedia Subsystem (IMS)-based solutions, with a focus on IMS-powered applications and security solutions. Sonus participated at the IMS Forum Plugfest III, hosted by the IMS Forum (www.IMSForum.org) and held at the University of New Hampshire InterOperability Lab in Durham, N.H.

Sonus provided the core components of one of the reference testbeds using its Session Control function, SRX, and its sophisticated subscriber database solution, HSX. In addition, among the applications Sonus tested at Plugfest III were its Any-to-Any messaging solution, an application that transforms an incoming message of any format (Instant Message, SMS/MMS, etc.) to a form the recipient prefers (SMS, IM, email, etc.), bringing new levels of customization and personalization to the communications experience, as well as its Broadband-Mobile Convergence (BMC) solution. These applications were built using Sonus' recently released IMX™ 2.0 Multimedia Application Platform, an IMS-compliant SIP application server. Sonus also participated in a variety of tests designed to verify the security of IMS networks.

"Sonus has been a proud participant and sponsor in the Plugfest since the inaugural event a year ago. It is really encouraging to see how much progress has been made in such a short amount of time," said Vikram Saksena, Chief Technology Officer, Sonus Networks. "Sonus Networks is committed to helping our customers navigate the path to IMS, and successful participation at the Plugfest events provide a strong validation of our strategy."

"The ability for IMS applications to change end-user experiences is one of the reasons that there is so much interest in advancing adoption quickly, and Sonus is at the forefront of innovation in IMS-compliant application development," said Michael Khalilian, IMS Forum Chairman & President. "The Plugfest gives vendors like Sonus the opportunity to harden their IMS solutions in a rigorous, multi-vendor testing environment."

The IMS Forum's IMS Plugfest III is the third in a series of events designed to foster interoperability and certification for IMS services and applications. IMS Plugfests allow service providers to quickly realize revenue from their IMS investments by significantly reducing the time to market for new services and applications. The Plugfest testing events are creating industry-recognized interoperability test plans for IMS applications and services, allowing service providers to expedite IMS service rollout.

Plugfest III, “A Network of Services” focused on realizing applications and services delivered over the IMS and NGN network in the following areas:

• IP-voice, Instant Messaging, and BMC using femto-cells;
• Video Sharing and Multimedia;
• Services for Businesses and Unified Communications;
• User and Application Profile Handling;
• Delivery of IMS Core Services to 2G/3G Mobile Devices; and
• Security, Reliability and Robustness Testing for IMS Services.

The Sonus IMS-based solution tested at the Plugfest is the same platform currently available for deployment in customer networks today.

About the IMS Forum

The IMS Forum^® is a global, non-profit industry association devoted to interoperable IP Multimedia Subsystems and NGN services and solutions. IMS Forum's mission is to accelerate the interoperability of IMS applications and services, enabling enterprise and residential consumers to quickly benefit from the delivery of quadruple play voice, video, internet and mobile content over broadband cable, wireless and fixed networks. The IMS Forum is the initiator and organizer of IMS Plugfest^™, the industry's only event focused on IMS services interoperability verification and certification.

Through its Plugfests, working group interaction, and other activities, forum members are able to develop cost-effective multi service delivery platforms for IP services over wireline, cable, 3G, WiFi and WiMAX networks. For additional information or to join the IMS Forum and the IMS Plugfest IV, please visit www.IMSForum.org.

About Sonus Networks

Sonus Networks, Inc. is a leading provider of IP-voice 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 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 Sonus' Quarterly Report on Form 10-Q for the period ended September 30, 2007, filed with the SEC, 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 restatement of its historical stock option granting practices and accounting including regulatory actions or litigation; 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, Inc. All other company and product names may be trademarks of the respective companies with which they are associated.