Yahoo! and Microsoft are making their instant messaging systems capable of communicating with each other to create a communications platform with some 350 million user accounts.

The interoperability — the first of its kind between two distinct, global consumer IM providers — will form the world’s largest consumer IM community and be three times the size of Skype, the current leading VoIP application online.

Skype, which was bought by eBay last year currently has 100 million customers compared to Microsoft's 240 million and Yahoo's 110 million.

Launched today as a Beta, members of the test program will be able to talk freely with contacts on either service either via instant messaging or VoIP phone calls.

Yahoo! and Microsoft plan to make the interoperability between their respective IM services broadly available to consumers in the coming months.

However the both companies have said that they will continue to fight for new customers.

The deal leaves out the other two big instant messaging players in the market, Google and AOL, to fend for themselves.