Sonus Networks Contacts:
Media Relations:
Beth Morrissey
978.589.8579
bmorrissey@sonusnet.com

Investor Relations:
Jocelyn Philbrook
978.589.8672
jphilbrook@sonusnet.com

Epana Networks Contacts:
Media Relations:
Ronen Glimer
212.931.8738
rglimer@epana.com

Investor Relations:
Meryl Ravitz
212.931.8755
mravitz@epana.com

EPANA NETWORKS DELIVERS INTERNATIONAL PREPAID CALLING SERVICES
ON SONUS NETWORKS VoIP INFRASTRUCTURE

SIP Solutions Enable New York-based Carrier to Provide Highly Competitive Prepaid Offering

WESTFORD, MASS., (May 13, 2003) – Sonus Networks (Nasdaq: SONS) and Epana Networks
today announced that Epana has deployed Sonus’ packet voice infrastructure solutions to
support the delivery of international and domestic prepaid calling services. Epana’s voice over
IP (VoIP) network is commercially operational and has been carrying voice traffic since
September 2002.

“ We are focused on providing next-generation telecommunications solutions that deliver greater
value to our customers,” said Elie Seidman, founder and CEO, Epana Networks. “The packet
voice network that we have implemented with Sonus is helping us to achieve that goal and
enabling us to offer highly flexible prepaid calling services at extremely cost-effective rates.”

At the foundation of Epana’s VoIP network are Sonus’ Open Services Architecture™ (OSA) and
voice infrastructure solutions, including the GSX9000™ Open Services Switch, the Insignus
Softswitch and the Sonus Insight Network Management System. Additionally, Epana has
implemented a complete SIP-based prepaid calling card solution from Sonus’ Open Services
Partner Alliance (OSPA) members Pactolus Communications Software Corporation and
Convedia Corporation. Epana has deployed Pactolus’ SIPware™ Prepaid Calling Card
application and RapidFLEX™ Application Server in conjunction with Convedia’s CMS-6000 and
CMS-1000 Media Servers. With the Sonus VoIP infrastructure and enhanced services
applications in place, Epana calling card users can place domestic long distance calls, as well
as international calls to Asia, Africa, the Middle East and Latin America, at extremely
competitive rates.

“ Epana’s network implementation underscores the power of voice over IP in providing a flexible,
reliable and cost-effective alternative for deploying enhanced services applications such as
prepaid calling,” said Michael O’Hara, vice president, marketing, Sonus Networks. “We are
pleased that Epana chose Sonus as its partner in building out its next-generation voice network,
and we look forward to building on the success that we have already achieved together.”

About Epana Networks
Epana Networks is a facilities-based telecommunications service provider delivering a range of
industry-leading prepaid calling card services. Epana provides prepaid services for wholesale
and retail customers to over 200 countries worldwide. Leveraging its private fiber network,
Epana delivers high quality, low cost telecommunications services to customers across the
country and around the world. For more information, visit www.epana.com or e-mail
info@epana.com.

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 (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.