Internet service provider Earthlink wants to make a really big splash in the voice-over-IP (VoIP) space.

Since June 30, the Atlanta-based ISP has been quietly beta-testing its own next-generation online calling software called "Vling" -- a softphone based on the Session Initiation Protocol (SIP) that allows anyone to make unlimited PC calls. Now, Earthlink is finally ready to make some noise.

Up to this point, the company's VoIP offering primarily consisted of a service dubbed "Earthlink Unlimited Voice," which is really powered via a reseller agreement with Vonage. But five months ago, Earthlink's engineers went out in search of developers capable of delivering a proprietary, customizable client and stumbled upon SIPfoundry, the not-for-profit open source community that is seeded in part by Pingtel, the leading provider of open source, enterprise-class communications solutions.

"We are very much like what Red Hat is to operating systems," explained Al Brisard, VP of marketing at Pingtel.

Based on its sipXtapi project hosted at SIPfoundry, Pingtel developed a full-featured, standards-based SIP user agent based on Earthlink's technical specifications. The company said its SIPxua fills a critical market gap by delivering a complete solution simple API interface, SIP stack, media processing, and session processing for OEM applications.

On Monday, Pingtel will annouce that Earthlink is the first service provider to deploy the new software bundle, called SIPxua (pronounced SIP-X-U-A). In addition, Pingtel will announce that it is making the standards-based user agent platform, designed entirely in open source, generally available for other service providers, enterprise applications vendors and hardware vendors to deliver enterprise-grade VoIP solutions as part of services offerings or embedded in applications or hardware.

"It's a fundamental building block package. It's got a robust API on top of it; a full SIP stack; you can even plug a video codec to it," Brisard told TMCnet.

Pingtel's announcement involving Vling comes just one week after Earthlink's Skype-type service was mentioned by Google when it unveiled its much-publicized Google Talk. Google is currently working with Earthlink to enable its IM platform, which is based on Jabber's Extensible Messaging and Presence Protocol (XMPP), to interoperate with Vling's proprietary technology by building an XMPP gateway. (Aside from Vling, Earthlink doesn't have an IM client.)

"VoIP services are changing the way consumers communicate, and Vling provides a sleek and easy-to-use interface for people to make a voice call to any SIP-based user, worldwide," said Steve Howe, EarthLinks vice president of voice services. "To deliver such a service, we need an enterprise-grade provider to work with, and Pingtels flexibility, overall solution quality and adherence to SIP standards make them the obvious choice."

Earthlink's ability to easily integrated IM capabilities into Vling is directly attributed to the building blocks delivered in SIPxua, Brisard said. In fact, that was one of the key customization requirements that Earthlink requested that differentiates SIPxua from the entirely open source projects found at SIPfoundry.

"It's got some hooks to make enhancements to IM if someone were to build on top of it," the Pingtel official said.

Combined, Vling and the Vonage-powered Unlimited Voice could represent the beginning of an effective VoIP initiative for Earthlink. In addition, Earthlink announced in June that it entered a line-powered voice service agreement with Covad to conduct joint market trials of VoIP services in Dallas, San Francisco and San Jose and Seattle, beginning in October.

Earthlink confirmed to TMCnet that Vling will officially launch later this year in the fourth quarter. While the Vling service is currently restricted to only SIP-to-SIP calling, it is expected to have SIP-to-PSTN calling capabilities shortly.

"If not at launch, it will be shortly after," said Jerry Grasso, director of corporate communications at Earthlink.

Internet users interested in EarthLinks Vling can download the beta of the product at http://www.earthlink.net/voice/vling. Users do not need to be Earthlink ISP customers.

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Robert Liu is Executive Editor at TMCnet.Previously, he was Executive Editor at Jupitermedia and has also written for CNN, A&E, Dow Jones and Bloomberg.For more articles, please visit Robert Liu's columnist page.