VOIP service works with cable, DSL EarthLink is looking to drum up more revenue from its high-speed customers by offering an Internet phone service, which will allow subscribers to make unlimited local and long-distance national calls for $39.99 a month.The ISP (lnternet service provider) officially plugged in the new service, dubbed EarthLink Unlimited Voice, Thursday, hoping to further tap into its growing base of high-speed customers who already pay $41.95 to $49.95 for monthly Net access.The phone service includes free voicemail, call waiting, call forwarding and caller ID and blocking, as well as unlimited free calls to Canada and discount international rates. The service will be provided by Vonage Holdings, which confirmed a deal with the ISP last month.The voice-over-IP (VoIP) offering works with either cable or digital subscriber line (DSL) connections, and the company said that it would also throw in the necessary hardware for free. Customers use a standard router to split their broadband connections between their modem and an analog telephone adapter (ADA) box, EarthLink said. Users then plug a touch-tone phone into the ATA box.The new paid offering comes as the company scrambles to bolster its revenue during difficult economic times. The ISP laid of 25 percent of its staff in January, with cuts taking place in the customer service and technical support areas. The Atlanta, Ga.-based company points to its growing number of high-speed customers as a bright spot, however, giving it an opportunity to bundle paid services with broadband access. EarthLink currently claims 779,000 high-speed subscribers. Software DevelopmentTechnology Industry