Microsoft is now sending emails to all its 100 million+ Messenger users to confirm that the Messenger service will officially be retired on March 15, 2013. All users will be migrated to Skype and the users won't be able to sign in to the Windows Live Messenger.
The would continue to work in China past March 15th, due to the service being handled by a third party company in that country.
Messenger users have to download and install Skype and sign in using their Microsoft Account, and their Messenger contacts will be available in Skype.
Update: it turns out, Microsoft won't kill its Messenger service on March 15!
Edited by Liskiller, 12 January 2013 - 04:34 AM.