Since Microsoft bought Skype, the VoIP client saw its userbase rise from 180 million to around 280 million monthly active users. Windows Live Messenger on the other hand saw a big decline in user activity, Microsoft now cites a monthly active user figure of only 100 million users, not even a third of the 330 million active users the service had on its tenth anniversary in 2009.
Switching from Windows Live Messenger to Skype only involves downloading the latest Skype client, you can log in with your Microsoft account and all your Messenger contacts will be in place.
And Microsoft wants to juice its Skype product, for which is paid $8.5 billion; It is now key to understand Skype not as a VoIP product, or a video calling service, but instead the communications layer that Microsoft intends to bake into its every product, and extend to rival platforms whenever possible.Source: The Next Web
Just as Bing is not simply a search engine, but is the search and sort tool that Microsoft is implementing across its products – powering app store searches, for example – so too is Skype now more platform than single product.