If you use the Yahoo! Messenger iPhone app, a new version released yesterday now supports the ability to chat with your Windows Live contacts, according to a post on the Yahoo! Messenger Blog dated April 4th.
Now when you’re on your iPhone, your Windows Live friends will be able to see when you’re online, and send and receive messages from them. You can also add new Windows Live friends right from the app.
You should be prompted to update your Yahoo! Messenger iPhone app through iTunes, or you can download the app through iTunes.