iOS 8: Wi-Fi Calls or iPhone Cellular Calls

iOS 8 brings two features that are mutually exclusive: Wi-Fi Calls and iPhone Cellular Calls.

Wi-Fi calling will be turned off to allow other devices to make and receive calls through your iPhone.

iPhone Cellular Calls or Wi-Fi Calling

Wi-Fi Calls is currently enabled on carriers that support the feature, such as T-Mobile USA.

T-Mobile Wi-Fi Calls e911 Address

iOS 8 also enables Cellular Calls handoff to OS X Yosemite and other iOS 8 devices.