Microsoft and Yahoo announced today that they're officially unifying both instant messengers, allowing users of both platforms to communicate w/ the other.
Though there are already a plethora of 3rd party multiplatform messengers, this will allow users to use the original manufacturers software, (which has been a pet peeve of mine) and have friends and users from both platforms on one list.
The companies have said the purpose is to have the largest IM community w/ the combination of both clients totaling around 350 million users.
Initially the companies intended to release the feature as a limited beta, but have since reneged on that idea altogether, opening the products to anyone who is interested in dabbling w/ the new clients. In order to have the functionality, all you need to do is visit the respective Yahoo & MSN sites, sign new user agreements and download the latest versions of the IM Clients, and you're good to go!!