Recently, Apple released iOS 12.2 which provides support for the FirstNet Wi-Fi calling and RealTime Text (RTT) features. WiFi calling uses an available WiFi network to place your call over the Internet. Clearly, if you don't have a cellular signal or it's spotty, the ability to make WiFi calls comes in handy. Supported devices are iPhone 6S and newer. To take advantage of these features, customers need to update their iDevice to iOS 12.2:
To update the Apple device software
1. Connect the device to Wi-Fi. The device must be connected to Wi-Fi for updates.
2. Tap Settings, tap General, and then tap Software Update.
3. Tap Install Now.
Note: Tap Continue or Cancel if you see a message asking whether you want to temporarily remove apps to create more space for the update. When the update is complete, the apps will automatically be reinstalled.
4. If prompted, enter your passcode.
Note: Some devices may require a series of updates to support Wi-Fi calling
To enable Wi-Fi Calling on your Apple device
1. Tap Settings, tap Phone, and then tap Wi-Fi Calling.
2. Turn Wi-Fi Calling on This iPhone On
3. Tap Continue to acknowledge Important Information for FirstNet Subscribers
4. Enter or confirm your address for emergency services