Obviously carrier support is not needed to do VoIP over WiFi, but what TMo and Rogers offer is their own VoIP over WiFi seamlessly integrated with the cellular calling feature. You don't need to use a separate app for dialing like you would with Skype, just dial normally and the phone will pick the best network to make the call. Also, it will use your cell number. Up until now the feature was only supported on a very limited number of phones.
6/3/14 at 3:14pm