So as of this morning, like many OP6 users I found that my phone was no longer connected to the AT&T network. AT&T had been helpful, they disabled my SIM and enabled the SIM on a refurbished Galaxy S9 (no thanks).

This lead to a call to AT&T customer service, after speaking with a very nice lady with AT&T, she was able to confirm my OP6 IMEI, confirm the G9 IMEI, and add my OP6 IMEI to their network again. This also involved activating the new SIM.

After about five minutes I was instructed to reboot my phone, I did and just like that I was on LTE calling without any problems (VoLTE). I’m not sure how long this will last but at least I can continue to use my OP6 until I’m ready to upgrade to something different.