New XOptions Flex Leverages Sonus' Carrier-Grade Solutions to Deliver Enhanced Next Generation IP Services to XO's Business Customers

CHELMSFORD, Mass., January 31, 2005 -Sonus Networks (Nasdaq: SONS), a leading supplier of service provider voice over IP (VoIP) infrastructure solutions, announced today that XO Communications, Inc. (OTCBB: XOCM.OB) is rolling out XOptions® Flex, the first in a series of the carrier's new enhanced services delivered over the XO national IP network and Sonus Network technology. Leveraging the Sonus Open Services Architecture™ (OSA), XO Communications will deliver a broad range of IP telephony applications and features to businesses throughout the United States.

"XO Communications was one of the first carriers to recognize the benefits of a VoIP architecture. Since selecting Sonus as the platform for their next-generation network, they have significantly expanded their network and telephony services," said Steve Edwards, chief marketing officer, Sonus Networks. "XO Communications' new XOptions Flex service is a value-add to their customers, and a great example of the types of enhanced next-generation services that are changing the way businesses think about their communication needs. We are extremely proud to have worked with XO to develop this network, and we look forward to continuing to support their endeavors with one of the most scalable and reliable VoIP solutions in the industry."

XO Communications launched their Sonus-based network in 2001 and over the last four years has continued to expand their deployment. Today, the company carries 600 million minutes of customer long distance traffic each month across its IP network. Continuing to build on its industry leading position, XO Communications will rollout XOptions® Flex in Boston, New York and Washington, DC in early March followed by full nationwide availability in the second quarter. The new service combines local, long distance, Internet access and web hosting services for one flat monthly rate on a single bill. XO offers these services over a single broadband connection, which allows customers to dynamically allocate capacity to voice and data traffic.

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 ArchitectureTM  (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 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' Annual Report on Form 10-K/A dated July 28, 2004 and filed with the SEC, and the "Cautionary Statements" section of Sonus' Quarterly Report on Form 10-Q, dated November 9, 2004 and filed with the SEC, which identify important risk factors that could cause actual results to differ from those contained in the forward-looking statements. 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 and Insignus are trademarks of Sonus Networks. All other trademarks, service marks, registered trademarks, or registered service marks are the property of their respective owners.