The move, if the search company can build user momentum for its own client software, could prove a catalyst for globally interoperable, standards-based instant messaging and voice over IP.

From yesterday, and instant messaging server that supports the XMPP protocol will be able to interact with Google Talk’s network, and vice versa. Google also reaffirmed its commitment to implement SIP, but would not give a timeframe.

We already had support for any XMPP client to connect to our network, so users had the choice of clients, said Google Talk product manager Mike Jazayeri. This is the server-to-server part, so if you have an account on the Google Talk network you can talk to clients on any other federated XMPP network, and vice versa.

XMPP, the extensible messaging and presence protocol, came out of the Jabber Software Foundation’s open source Jabber project. It was ratified as an Internet Engineering Task Force standard in 2004.

The protocol allows IM to function much like email. Users send messages through their XMPP server, which acts a bit like an SMTP server. These XMPP servers find each other using the DNS, but using the SRV record instead of the MX record.

We want to help make IM and VoIP as interoperable as email and telephones, Jazayeri said. He added that support for interoperable VoIP is made possible due to implementation of the Jingle protocol, a pre-standard extension to XMPP.

Currently, Google says that Talk will now interoperate with IM services provided by Earthlink, the Gizmo Project, Tiscali, Netease, Chikka, MediaRing, and thousands of other ISPs, universities, corporations and individual users.

The three biggest IM networks are operated by AOL, Yahoo and Microsoft, none of which are on that list. Getting those guys on board should be considered essential before any claim of global interoperability can be made.

Currently, Yahoo and Microsoft are connecting their networks, and expect to go live this spring. Microsoft is a strong supporter of SIP and SIMPLE, IETF-approved alternatives to XMPP, due to its Live Communications Server implementation.

Rather than just throwing open the doors to federation, the Microsoft-Yahoo deal has a business model backing it, the terms of which have not been disclosed.

Google’s potential trump card is its recent billion-dollar investment in Time Warner subsidiary AOL, which includes a clause to work to connect AOL Instant Messenger and Google Talk, provided certain conditions are met.

Those conditions have not been disclosed. AOL, when it was in a stronger negotiating position, had previously been reluctant to connect AIM to other IM systems, proclaiming security and stability concerns.

Jazayeri said that the time between Google Talk’s launch last August and today has been used to test the service for security and load, but added that this week’s news is unrelated to the AOL deal. Google will encourage all our partners to use XMPP, he said.