LOS ANGELES, CA — December 15, 2004— Mpower Communications Corp. (AMEX:MPE), a leading provider of broadband high-speed Internet access and local and long distance voice services, today announced that it has been selected by Cardenas Markets Inc. to provide communications services to nine of its locations and the company’s corporate headquarters.

Under the terms of the two-year agreement, Mpower is supplying phone and data communications services to connect Cardenas Markets’ supermarket and restaurant locations across southern California. Cardenas Market utilizes Mpower’s high speed Internet access to quickly and securely transfer real-time sales figures, pricing and advertising updates between stores and the company’s headquarters. With free LATA wide calling from Mpower, Cardenas Markets is able to place calls between stores, customers and suppliers – most of which are located in Mpower’s free calling area – for no additional cost.

“We wanted to consolidate our services and reduce our expenses without compromising service, so we decided to go with Mpower,” said George Cardenas, Vice President of Information Systems at Cardenas Markets. “We switched over 116 voice lines and added high-speed dedicated data connectivity across nine locations without any hurdles. Mpower’s sales and service reps worked very hard for us and did everything necessary to meet our expectations. This was the easiest, most effective cost cutting and productivity improving decision we have made in a long time.”

Jim Ferguson, President of Sales and Marketing for Mpower added, “After dealing with several different phone companies, we are pleased that Cardenas Markets has recognized the power and value in working with a single provider and is reaping the benefits of our free local calling and high-data services in operating its business more efficiently.”

About Mpower Holding Corporation
Mpower Holding Corporation (AMEX:MPE) is the parent company of Mpower Communications, a leading facilities-based broadband communications provider offering a full range of data, telephony, Internet access and Web hosting services for small and medium-size business customers. Further information about the company can be found at www.mpowercom.com.

Forward-Looking Statements
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