Skype 1.0 for Windows Phone lets you make Skype video and voice
calls over 3G and WiFi, search for and add contacts, and make
calls to landlines. However, no one can call you via Skype unless
you have the app open and running on your phone. Unlike Android
and iOS, Skype needs to be your active app in order to receive
calls as there is no background functionality at all in the app.
Microsoft should just buy Skype so they can make sure the Windows Phone version is top-notch.