Microsoft and Yahoo! IM working in unison

Nine months after announcing they would make their instant messaging services interoperate, Microsoft and Yahoo! have done it.

The companies are set to today release a limited beta test of a service that will enable users of Windows Live Messenger (the next generation of MSN Messenger) and Yahoo! Messenger with Voice to connect with each other.

The move creates a global community of nearly 350 million accounts, the companies said. The beta service is being launched globally in 15 localised languages.

Blake Irving, corporate vice president in Microsoft's Windows Live Platform division, said on Wednesday: "It's the first-ever bridge between two global instant messaging services."

The service will allow people to sign into both services using one user ID, and to see the status of connections of friends from both networks.

Brad Garlinghouse, senior vice president of communications, community and front doors at Yahoo!, said: "The messenger friend list is your heart of your social network in many ways. We expect a rapid ramp with millions of users in the coming weeks."

Connecting the networks took months of testing, Irving said: "This was a very difficult technical problem to solve."

The companies announced plans last October to make their IM services interoperable, in what analysts said was a shot to market leader AOL Instant Messenger and a defensive jab against Google Talk.

AOL representatives could not be reached for comment.

A Google representative provided an email statement that said: "From the very beginning, the Google Talk service was built to support interoperability with hundreds of other communications service providers. Any service provider that supports industry standard protocols can federate with us today, and many have... We don't have further details to share on our future plans in this area at this time."

Under an agreement between AOL and Google, in which Google paid $1bn for a five per cent stake, the two companies are working to make their respective instant messaging services interoperate.

Neither Microsoft nor Yahoo! would comment on the status of any discussions with AOL about interoperating.

Yahoo!'s Garlinghouse said: "We certainly welcome seeing other industry players come to the table. We're blazing a trail for how interoperability is done."

David Card, an analyst at JupiterResearch, said AOL would not move to interoperate with others until customers demanded it.

He said: "AOL doesn't need to let the other guys in as long as the user base is still healthy. I think they will let people in, eventually. This will help pressure them a little bit more."

Elinor Mills writes for CNET News.com