The announcement was made via Skype blog:
We've got good news to share! Skype and Messenger are coming together. Millions of Messenger users will be able to reach their Messenger friends on Skype. By updating to Skype, Messenger users can instant message and video call their Messenger friends.
Our goal remains to deliver the best communications experience for everyone, everywhere. We want to focus our efforts on making things simpler for our users while continuously improving the overall experience. We will retire Messenger in all countries worldwide in the first quarter of 2013 (with the exception of mainland China where Messenger will continue to be available).
In a bid to get people on board with the move, Microsoft listed the various benefits of the move including: