Yahoo! and Microsoft today will begin limited public beta testing of interoperability between their instant messaging (IM) services that enable users of Windows Live Messenger, the next generation of MSN Messenger, and Yahoo! Messenger with Voice to connect with each other. This interoperability -- the first of its kind between two distinct, global consumer IM providers -- will form the world's largest consumer IM community, approaching 350 million accounts, according to the companies. A new version of the Mac Yahoo! Messenger 3.0b was released last week, and includes the new MSN Messenger integration. [updated with Mac compatibility info]

According to the release, consumers worldwide from Microsoft and Yahoo! will be able to take advantage of IM interoperability and join the limited public beta program, allowing them exchange instant messages across the free services as well as see their friends' online presence, view personal status messages, share select emoticons, view offline messages and add new contacts from either service at no cost.

Both companies said that they plan to make the interoperability between their respective IM services broadly available to consumers in the coming months, although did not provide a specific date.

"This first-of-its-kind interoperability between consumer IM leaders Microsoft and Yahoo! gives our customers tremendous control, convenience and freedom in their Web communication experiences with Windows Live," said Blake Irving, corporate vice president, Windows Live Platform at Microsoft. "We're proud to deliver this latest advancement in IM services that empower people to communicate with virtually whomever they want, wherever they want and whenever they want."

Windows Live Messenger and Yahoo! Messenger with Voice users in the U.S. and more than 15 international markets can register to participate in the IM interoperability beta by visiting Yahoo!. The new beta program will be available in Argentina, Australia, Brazil, Canada (English and French), China, France, Germany, Hong Kong, India, Italy, Korea, Mexico, Netherlands, Singapore, Spain, Taiwan, Turkey, the United Kingdom and the United States (English and Spanish).