I was not in one of the service areas affected last week, but on Wednesday (2/21) after several attempts to send a text the fourth time it worked. Then on Saturday (2/24) a text didn't go through the first time, but then did. I've gotten an SOS on my iPhone 13 mini a couple of times since but following the advice below managed to get rid of it. Now it just won't go away. AT&T? Latest update from Apple which I installed recently 17.3.1 I detest, actually. I only install updates after they've been out at least a week and I've checked forums for complaints - but this one is ugly and intrusive. Bleah!
Main point - I now have no cell service, have done all suggested actions outside of AT&T (I'll go to our local store later today) and it's Wednesday (2/28). Maybe some of these critics of hysteria would like to comment on this!!!