According to the the german gaming magazin "Gamestar" T-Mobile is going to block the Skypefunction on their networks and hotspots. Officialy they blame the heavy traffic this service causes. But some people think that this is just an excuse.
Maybe Orange and O2 will also behave like this?
Source: http://www.gamestar.de/hardware/news/vermischtes/1955147/skype_greift_telekom_an.html