Make calls using Wi-Fi on iPhone
When your iPhone has a low cellular signal, use Wi-Fi Calling to make and receive calls through a Wi-Fi network.
Go to Settings
> Cellular.
If your iPhone has Dual SIM, choose a line (below SIMs).
Tap Wi-Fi Calling, then turn on Wi-Fi Calling on This iPhone.
Enter or confirm your address for emergency services.
Note: Emergency calls on your iPhone are routed through cellular service when available. In the event that cellular service isn’t available, and you have enabled Wi-Fi Calling, emergency calls may be made over Wi-Fi, and your device’s location information may be used for emergency calls to aid response efforts, regardless of whether you enable Location Services. Some carriers may use the address you registered with the carrier when signing up for Wi-Fi Calling as your location. When connected to Wi-Fi calling, your iPhone may not receive emergency alerts.
When Wi-Fi Calling is available, “Wi-Fi” is displayed after your carrier name in the status bar, and all your calls go through Wi-Fi.
Note: If the Wi-Fi connection is lost when you make calls, calls switch automatically to your carrier’s cellular network using VoLTE (Voice over LTE), if available and turned on. See View or change cellular data settings. (VoLTE calls also switch to Wi-Fi when a Wi-Fi connection becomes available.) Contact your carrier for feature availability.