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apanese Carrier Achieved 2 Million Subscriber Goal Months Ahead of Plan

WESTFORD, Mass., June 10, 2003 – Sonus Networks (Nasdaq: SONS) today announced that the Fusion Communications next-generation voice over IP (VoIP) network now supports more than 2.3 million subscriber lines. Fusion launched its Sonus-based network in April 2001 with 150,000 subscribers, and over the two years has increased the number of business and residential customers by more than tenfold.

"The success of the Fusion network has surpassed all expectations," said Michael O'Hara, vice president, marketing, Sonus Networks. "Since launching their service, they have steadily increased the number of subscribers, and they reached this significant milestone more than four months ahead of plan. We are extremely proud to share in Fusion's success and look forward to working with them to grow their network and introduce new services to their subscribers."

Founded in March of 2000, Fusion was the first competitive carrier to challenge the Japanese incumbent carriers following the passage of telecommunications deregulation earlier that year. Fusion was also the first carrier in Japan to deploy a pure IP-based network that supports both voice and data. Fusion has implemented Sonus' GSX9000(TM) Open Services Switch, the Insignus(TM) Softswitch and the Sonus Insight(TM) Management System as the foundation of its next-generation voice network. With the Sonus systems, Fusion has been able to differentiate itself in the market by offering long distance, international, toll-free and PRI access services at highly competitive rates.

Fusion has implemented the Sonus voice infrastructure solutions in 18 locations distributed through Japan, with plans to expand the network further. While traditional voice services comprise the bulk of Fusion's business, the carrier is planning to augment these services by delivering new IP-based enhanced services.

About Sonus Networks

Sonus Networks, Inc., is a leading provider of packet voice infrastructure products for the new public network. With its Open Services Architecture(TM) (OSA), Sonus delivers end-to-end solutions addressing a full range of carrier applications, including trunking, residential access and Centrex, tandem switching, and IP voice termination, as well as enhanced services. Sonus' award-winning voice infrastructure solutions, including media gateways, softswitches and network management systems, are deployed in service provider networks worldwide. Sonus, founded in 1997, is headquartered in Westford, Massachusetts. Additional information on Sonus is available at http://www.sonusnet.com.

This release may contain projections or other forward-looking statements regarding future events or the future financial performance of Sonus 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' Annual Report on Form 10-K, dated March 19, 2003 and filed with the SEC, which identifies important risk factors that could cause actual results to differ from those contained in the forward-looking statements. These risk factors include, among others, the adverse effect of recent developments in the telecommunications industry, the weakened financial position of many service providers, Sonus' ability to grow its customer base, dependence on new product offerings, market acceptance of its products, rapid technological and market change and manufacturing and sourcing risks. In addition, 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.

GSX9000, Insignus, Sonus Insight and Open Services Architecture are trademarks of Sonus Networks. All other trademarks, service marks, registered trademarks, or registered service marks are the property of their respective owners.