I opened a case and went through the support levels and finally reached a senior advisor. The lower level support people were still advising to do the 90 minute Do Not Disturb routine, and I told them it does not work. Another option the lower levels gave me was they would send me a new phone with a hold on my account until I sent mine back, and charge me $29 for shipping. I laughed.
Anyway, the senior advisor gave me his contact info, and also said he would contact me when the proper fix had been determined, and that I would not be paying a penny. They are definitely aware of, and are working on, the problem. He advised to not return the phone for replacement at this time, and did not have an answer yet as to whether it is a hardware or software issue. Since I opened my support case within the 14 day return window, I feel fairly confident that I will be taken care of. Assuming, of course, that they can figure out and correct the problem. 64 gig space gray from the AT&T store, C3 factory, and I forget the manufactured week, but that doesn't seem to matter anyway.