The network signal will be weak in some places yet the speed of the internet will be strong. Particularly for places like those, WiFi calling had been introduced. WiFi calling is similar to normal voice calling, but the call will be placed through the WiFi network instead of the carrier’s network.
To make a call through WiFi on Android phones,
Step I: Open Settings → Connections.
Step II: Click “WiFi Calling” and turn it on.
To make a call through WiFi on iPhones,
Step I: Go to Settings → Cellular.
Step II: Tap “WiFi Calling” and click “Enable”.
Always make sure to turn on WiFi before setting your phone for WiFI calling.