Open Federation has come to Google Talk. What's that? According to a post on the Google Blog, Google Talk is now full interoperable (capable of communicating with any other service) using the XMPP protocol (Extensible Messaging and Presence Protocol).
From the Blog post:
With open federation, you get to choose your service provider and you can talk to people on any other federated service (and vice versa). In addition to the Google Talk service, many other companies, universities, and corporations support open federation today. This means you can now talk to millions of users around the world all with a single account on the service provider of your choice.
Services using this protocol include Earthlink, Gizmo Project, Tiscali, Netease, Chikka, MediaRing, and thousands of other ISPs, universities, corporations and individual users.
Of course, the recent Google/AOL deal said that eventually (no dates at this time) Google Talk and AOL's AIM will offer interoperability. We also know that MSN and Yahoo have announced plans to make their IM services interoperable.