As of yesterday, Google Talk now federates with other XMPP services. Google announced "open federation" for the Google Talk service allowing people on different IM/VoIP clients to "talk" to each other. Google Talk currently support open federation with any service provider that supports the Extensible Messaging and Presence Protocol (XMPP) standard. This includes Chikka, Earthlink, Gizmo, Tiscali, MediaRing, as well as universites, corporations and individual users that setup their own XMPP-compliant servers.
Google Talk's Gary Burd "flipped the switch" to connect the Google Talk service to the public XMPP network and gleefully takes pride in the fact that he got to "throw the switch" (good thing he doesn't work for the prison system! ;) ) Gary Burd writes in the Google Talk blog, "I'm proud to have worked on this, and to be the one that got to turn on something that lets Google Talk users talk to millions of other users out there."
The Google Talk blog writes:
I flipped the switch to connect the Google Talk Service to the public XMPP network this morning. Google Talk users can now chat with users on other XMPP services and vice versa.
If you want to connect your service to the Google Talk Service, you should know that Google Talk uses the dialback protocol as described in RFC 3920.
Please post to the Google Talk Open Group if you have any questions or problems with interoperability on the Google Talk Service.
I'm proud to have worked on this, and to be the one that got to turn on something that lets Google Talk users talk to millions of other users out there.