iPhone 6
Select help topic
Turning Wi-Fi calling on or off
When Wi-Fi calling is turned on, you can make and answer calls using a Wi-Fi network when you're in an area with little or no network coverage. To turn on Wi-Fi calling, you need to establish a connection to a Wi-Fi network and turn on 4G for voice calls and mobile data.
Press Settings.
Press Phone.
Press Wi-Fi Calling.
Press the indicator next to "Wi-Fi Calling on This iPhone" to turn the function on or off.
If you turn on the function, press Enable.
Press the Home key to return to the home screen.