Sonus-based Infrastructure to Support Callipso’s New Enhanced IP Offerings

CHELMSFORD, Mass. and SANTA ANA, Calif., March 30, 2004 - Sonus Networks (Nasdaq: SONS) and Callipso today announced that Callipso is implementing a nationwide, next-generation packet voice network with Sonus Networks.  Callipso is deploying Sonus’ Open Services Architecture (OSA) to deliver a range of voice over IP (VoIP) services, including origination and termination, as well as Session Initiation Protocol (SIP)-based enhanced services in to its existing nationwide, voice over IP network.

“Callipso is committed to providing innovative and reliable enhanced IP services that will add value to our customers’ businesses today and well into the future,” said Ted Dimmer, chief technology officer, Callipso.  “Sonus’ field-proven voice infrastructure delivers enhanced IP services that will allow us to differentiate ourselves and build loyalty among our customers, and also enable us to expand our business opportunities into new markets.”

To build out its VoIP network, Callipso is implementing Sonus’ core trunking solutions including the GSX9000 Open Services Switch, the Insignus Softswitch and the Sonus Insight Management System.  Callipso is currently deploying the Sonus infrastructure in five cities throughout the United States to enable a SS7 interconnection capability that will support nationwide voice services as well as SIP-based enhanced services such as prepaid calling, web-based audio conferencing and, in later deployment phases, hosted IP Centrex and IP PBX offerings.  Future network plans call for the deployment of Sonus’ Network Border Switching solution, which will enable Callipso to interconnect or “peer” with other domestic and international carriers using VoIP rather than circuit switching.

“Implementing innovative network technologies is a critical component of Callipso’s strategy,” said Michael O’Hara, vice president, marketing, Sonus Networks.  “As a leader in the VoIP market, Sonus has extensive experience developing feature-rich voice networks for service providers around the globe.  We are pleased to have been selected by Callipso for this network deployment and look forward to building a successful relationship.”

About Callipso

Founded in 1996, Callipso provides enhanced IP services to telecommunications carriers, enterprises and the prepaid card marketplace.  Callipso addresses today’s communications requirements with the industry’s leading enhanced IP services, for the first time bridging the gap between IT and telecom to enable user-defined communications. Callipso, a privately held company, can be found on the web at www.callipso.com.

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 Open Services Architecture (OSA), Sonus delivers end-to-end solutions addressing a full range of carrier applications, including trunking and tandem switching, residential and business access, network border switching and enhanced services. Sonus’ 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 Chelmsford, 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 “Cautionary Statements” section of Sonus’ Quarterly Report on Form 10-Q, dated November 10, 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.

Risk factors include, among others, adverse effects resulting from the delay in the completion and audit of its financial statements, the continued adverse effect of developments in the telecommunications industry, Sonus’ ability to grow its customer base, dependence on new product offerings, market acceptance of its products, competition from large incumbent vendors, 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.

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

Sonus Networks
Media Relations:
Beth Morrissey
978-614-8579
bmorrissey@sonusnet.com

Investor Relations:
Jocelyn Philbrook
978-614-8672
jphilbrook@sonusnet.com

Callipso
Media Relations:
Michele Shannon
714-668-4329
michele.shannon@callipso.com

MS&L
Dwyer Williams
312-861-5273
dwyer.williams@mslpr.com