When WiFi Calling is activated, you can make and receive voice calls over WLAN when you're in an area with poor or no network coverage. This service only works once you've received an SMS about Advanced Calling availability. Remember, you need to establish a connection to a WLAN.
Find "Wi-Fi Calling"
Press Wi-Fi Calling.
Activate or deactivate WiFi Calling
Press the indicator next to "Wi-Fi Calling on This iPhone" to activate or deactivate the function.
If you activate the function:
When WiFi Calling is active, the text "WiFi" next to the name of the operator is displayed.
Return to the Home screen
Press the Home key to end the session and return to the Home screen.