These are instructions on how to enable Wi-Fi Calling on the iPhone.
Wi-Fi Calling lets you place a phone call in an area with little or no cellular coverage using your Internet connection.
Step One
Tap to launch Settings from your SpringBoard.
Step Two
Choose Phone from the Settings menu.
Step Three
Select Wi-Fi Calling from the Phone menu.
Step Four
Tap to toggle the Wi-Fi Calling on This iPhone switch to the ON position then press the Enable to confirm your selection.
If Wi-Fi Calling is available, you'll see Wi-Fi after your carrier name in the status bar and your device will now make and receive calls over Wi-Fi.