Microsoft and Yahoo have announced that for the first time they will allow interoperability between the consumer versions of their IM (instant messaging) clients.

Last night the companies began offering limited public testing enabling users of Windows Live Messenger and Yahoo Messenger with Voice to connect to each other through either service. Users can register for the public beta here or here.

Once they gain access to the beta, users can exchange IMs across the two services, as well as see their friends' online presence, view personal status messages, share emoticons, view offline messages and add new contacts between the services.

Microsoft has already enabled IM interoperability between LCS (Live Communications Server), its enterprise unified messaging software, and IM clients from Yahoo and AOL, as well as its own Windows Live Messenger. Business customers that have purchased LCS and Office Communicator, the client interface for LCS, can connect to all of those IM clients. Yesterday marked the first time users of the free Windows Live Messenger and Yahoo IM clients could take advantage of interoperability between them, Microsoft said.

The beta program will be available in Argentina, Australia, Brazil, Canada, China, France, Germany, Hong Kong, India, Italy, Korea, Mexico, the Netherlands, Singapore, Spain, Taiwan, Turkey, the UK and the US.

Microsoft and Yahoo plan to make this interoperability available to all users of Windows Live Messenger and Yahoo Messenger with Voice in the next few months, the companies said.

Microsoft declined to comment directly on whether it would soon have a similar deal to make Windows Live Messenger interoperate with AOL's consumer IM client, but said that the company "anticipates more of these relationships in the future".

Windows Live Messenger is the latest incarnation of what was formerly MSN Messenger. Microsoft rebranded the product as part of its Windows Live online services plan and released the first version of Windows Live Messenger last month.