iPhone XR and Microcell tower

Use wifi calling

@bevslay - agreed. The MicroCell reached its EOL at the end of 2017. The service itself will be shutdown once AT&T begins to transition away from their 3G network. WiFi-C (WiFi Calling) is what is recommended now. If, for some reason, you want to use your XR with the MicroCell just add its phone number to the Approved Users List (unless it's the same phone number that was used to register/activate the MicroCell), save, shutdown your phone completely, and then after a few seconds, reboot your phone. The phone may need to register the MicroCell as part of its cellular neighborhood.

@bevslay - If you're gong to use WiFi-C then it's best to power off the MicroCell altogether. Sometimes the phone doesn't "know" which to connect to, the MicroCell or your WiFi, so call quality issues may develop. WiFi-C is dependent on your WiFi, it has nothing to do with the MicroCell.

If you need the MicroCell for other non-WiFi-C capable phones then you may need to place your XR in Airplane Mode to disable its cellular radio so it can't connect to the MicroCell, but you'll need to remember to disable Airplane Mode when you are out of range of the MicroCell.