iOS 8.0 beta 3, T-Mobile and WiFi Calling
Apple adds WiFi Calling to iOS 8.0 beta 3. At this point in time, T-Mobile is the only carrier in the USA that supports WiFi Calling feature.
I ask T-Mobile USA if currently they are supporting iOS 8.0 WiFi Calling. One T-Mobile USA representative adamantly stated that T-Mobile is not yet adding the support for iPhones, even though the feature is now built in iOS 8.0 beta 3.
WiFi calling is available on certain Android phones on T-Mobile USA network.