A few days ago we heard that Windows Live Messenger would be closed on March 15th, forcing all users to switch to using Skype to continue on their instant messaging paths. New information has arisen since then, though, that doesn't quite spell the end of the platform, as the actual back-end Messenger Service will not be shut down on March 15th, meaning that third-party clients will continue to work beyond that date.
Ars Technica heard from Microsoft that on March 15th the official desktop Windows Live Messenger client will be blacklisted from accessing the Messenger service, so the app will stop working and users will have to use Skype. However the back-end will continue to operate, allowing the client in Windows Phone to continue to work, presumably along with the Modern-UI client for Windows 8 and other third-party apps.
March 15th does represent the start of the full death of Windows Live Messenger though, as various parts will be decommissioned on following dates. In October 2013 support for the XMPP protocol will be retired, causing third party clients using this method of accessing Messenger to stop working. Following this, in March 2014 Microsoft's proprietary MSP protocol will cease to work, putting the final nail in Messenger's coffin.
Between now and March 2014, Microsoft should have integrated Messenger's infrastructure fully into Skype and transitioned all older clients to the new service. The good news in the meantime is that third-party clients will not immediately stop working in a few months, allowing more time for developers to switch to using Skype.
Source: Ars Technica