The VoIP service, Free Online Calling, is based on SIP, the session initiation protocol, and users will only be able to place calls to other people using SIP-based VoIP services.

EarthLink said it has peering relationships with two of the leading SIP-using VoIP service providers, SIPphone.com Inc and Pulver.com Inc’s Free World Dialup.

FWD’s Jeff Pulver wrote in his blog that EarthLink had approached Pulver about a partnership under which FWD would provide the VoIP infrastructure for the service.

Pulver wrote that he turned down the deal because EarthLink wanted FWD to carry the cost of scaling its infrastructure to support the new users and because the customers would remain EarthLink’s.

EarthLink said it will continue to offer its year-old flat-rate broadband telephony service, EarthLink Unlimited Voice, which enables IP calls to any phone over a broadband connection.