Microsoft have sent out a few million (100,000,00+) emails this week to its messenger users. It was sent out to let them know that on March 15th 2013, the messenger service will no longer be available. Microsoft are migrating everyone to Skype which it acquired in May 2011 for a tidy (little finger at corner of mouth) $8.5 billion. However, if you're in China, you can carry on using Messenger as Skype is operated by TOM who is the local provider there.
You can update to Skype by signing in with your Microsoft account which is the same and the users Messenger ID. The good news is all of the contacts in Messenger will be available in Skype. Messenger users will be given the option to merge accounts should you have both.
Microsoft did announce this earlier last year but said the exact date would be released in Q1 of 2013.