AT&T’s impotent network locks down SlingPlayer and Skype over 3G on the iPhone. You can easily jailbreak your iPhone 3G (or iPod touch) Using Tricker ThreeG, you trick apps into thinking a 3G connection is Wi-Fi. There’s a more involved process if you want to fool other apps too. You also need to install some custom text files for every app that you want VoIPover3G to trick your phone into thinking it’s running.”]
Source: https://gizmodo.com/how-to-hack-the-iphone-to-use-slingplayer-and-skype-ove-5254810