Microsoft's instant messaging and video chat are set for a major shake-up, with Microsoft announcing today that the Windows Live Messenger brand and client will be retired in the first quarter of 2013. They'll be replaced by the Skype client and Skype name everywhere, except for China, which will retain the Messenger naming.

On the front end, the transition from Messenger to Skype is happening surprisingly quickly. The Skype client added support for Messenger contacts and chat just two weeks ago, when version 6 was released. Within six months, the Skype client will be the only option available for connecting to Messenger contacts.

Behind the scenes, the migration has been underway for some time—in the opposite direction. As reported by ZDNet's Mary Jo Foley, the instant messaging back-end now uses a mix of Messenger's infrastructure and Azure cloud services.

Though the Skype client now connects to both Skype and Messenger networks (and Facebook too), the networks are at present still separate, and there's no bridging between the two. Messenger users signing in to Skype for the first time have to either merge their account with their own Skype account, or create a new Skype account if they don't have an existing one. Users of the Skype client can see both networks; Messenger clients, whether first- or third-party, will only see Messenger users.

The Skype client itself isn't an exact match for the Messenger client. Popular Messenger features such as "nudge" are absent, with only core IM and video chat functionality maintained. The loss when talking to Messenger contacts is partially offset by the gains when talking to Skype contacts: Skype permits video chatting on Facebook and with mobile clients, screen sharing, and for paying customers also offers calls to landlines and multi-person video chat.

The move to the Skype branding furthers Microsoft's move away from the Windows Live brand. While Windows Live Messenger once boasted three hundred million users, The Next Web is reporting this number as just one hundred million. Skype, conversely, has apparently picked up 100 million users since the Microsoft purchase, taking it to about 280 million monthly active users.