Leah Pearlmann has a blog post entitled The Final Chapter: Messenger + Yahoo which announces

And this month, this chapter of the story comes to a close. ANYONE using the latest version of Windows Live Messenger or Yahoo! Messenger (in most countries) will be able to add friends, send messages and select emoticons with those from either network like crazy – and we encourage you to do so!

 

People should be able to reach all their friends and family using just one IM service. Students should not have to use two IM services. NO ONE should have to give up watching American Idol for any reason.

Moral of the story: Windows Live and Yahoo! Messenger, holding hands to make the world a happier, better connected, Idol-istic place.

I've been taking a look at some of back end of how Yahoo! Messenger and Windows Live interop works as part getting my intern on how our platform works. I've been impressed by how smoothly this has been implemented as well as how some of the user interface complexities have been handled (e.g. what happens when you add a buddy who uses the same email address on both IM networks).

Kudos to Kitty and the rest of the team for getting this out of beta and bringing the dream of complete interoperability across the major IM networks closer to really.