As an AT&T user I’ve had some issues with my OP6 over the years. I had to get my IEMI registered with AT&T as a valid device on their network after the 3G shutdown so that I had access. Today randomly I discovered that I could no longer make calls (interestingly through google voice as well).

Basically I’d dial a number and hit the connect icon and it would say “Connecting…” and then dump me right back to the phone screen. I tried rebooting and clearing the phone cache. After that I tried to re-seating the nanoSIM without success.

I started poking around in the phone settings and I found that “use voLTE” was randomly disabled (who knows what happened). I enabled it and suddenly… nothing happened, I still couldn’t dial out (though strangely I could receive calls in).

I recalled that changing this setting required the phone to be rebooted, after that, success! I was able to dial out once more. So for any of you having the same issue:

Settings -> Wi-Fi & Network -> SIM & Network -> SIM 1

Under “ENHANCED COMMUNICATIONS” check the “VoLTE” “Use VoLTE when available” option and reboot the phone.