If you see the SOS Only message pop up on your iPhone, a simple restart or toggling Airplane mode on and off can help fix the issue.

What does it mean when your iPhone says SOS? Apple Support says if you see "No Service" or "Searching" in the status bar on your iPhone or iPad, your device isn't connected to a cellular network.

It also means there is a cellular network "available for emergency calls," Apple's support website states. AT&T outage: Why your iPhone may be stuck in SOS mode.