I am still having issues with clicking "Next" on the confirm your phone # screen. I did at one point get through it, but then I got the "it may take a few minutes..." screen like we are discussing, but then it sat on it for just over an hour. So I restarted the phone and I am back to square one with the Next button issue. Both the manual process and the process where you use your current iPhone to activate lead to the same issue.
Lol Apple or AT&T is botching this roll out. I'm in a thread on Twitter with multiple people saying the same thing. And yes, I've rebooted the new iPhone 12 Pro probably 20-30 times.