Yahoo! Inc. and Microsoft Corp. 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.1
Consumers worldwide from Microsoft and Yahoo! will be able to take advantage of IM interoperability and join the limited public beta program. They will be among the first to 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.2 Yahoo! and Microsoft plan to make the interoperability between their respective IM services broadly available to consumers in the coming months.
Source : Microsoft.com
For the Dutch Windows Live Messenger users … you need the localised (ie Dutch) version