A group of vendors have announced the formation of IMUnified, a coalition aimed at bringing interoperability to instant messaging services.

Notably missing from the roster, however, was industry giant America Online.

The coalition plans to introduce specifications by the end of August that would enable the implementation of functional interoperability among its members' instant messaging services.

IMUnified aims to support protocols developed by the Internet Engineering Task Force, it said in a statement.

With the exception of AOL, which operates two of the most popular Internet-based instant messaging services, the founding members of IMUnified include most of the leading players in the field as well as other technology companies.

The founding members of IMUnified are AT&T, Excite@Home, Icast, MSN, Odigo, Phone.com, Prodigy, Tribal Voice, and Yahoo.

AOL recently has come under fire from its rivals for not allowing users to exchange instant messages across the various services.