Yahoo! Messenger linked with MSN
The latest beta version of Yahoo! Messenger enables user to add Windows Live (MSN) Messenger contacts to their list. This means that people will be able to keep all their Yahoo! and MSN contacts in a single place, not needing to change IM clients in order to chat with their friends.
You can join the beta and test this for yourself. Your friends will need the new version for MSN as well. 
