To activate WiFi Calling, follow these steps:
Step 1: Insert U Mobile SIM into your iPhone.
Step 2: Activate the service. Text < WIFICALLING ON > via SMS to 28118.
Step 3: Enable WiFi Calling. Select Settings > Phone > Wi-Fi Calling > toggle to ON.
Step 4: Connect to a WiFi network.
Step 5: If WiFi Calling is activated, you will see “U Mobile WiFi”. All calls will then be made using WiFi Calling.