Do you live in southeast U.S.? Local iPhone users get no ATT signal. The same problems occur to T-Mobile, Verizon and Sprint coverage. All the biggest American carriers suffer strong outages recently and customers have to deal with the issues and wait until all the problems are solved.
Unfortunately you cannot fix AT&T outage southeast issue by ordering factory IMEI iPhone AT&T unlock since other major mobile operators also get the similar issues. Users of course wish to rely on their network and not get downtime errors while trying to use their mobile operator they are locked to or just subscribed to.
Unlocked iPhone users could at least select a different smaller company for a while but everyone who is locked to their AT&T or other network only have no choice but to sit and wait hoping for the positive results asap.
In case you get no AT&T coverate in area you might be locked to a different carrier. Use iPhone IMEI network checker to figure out what your original mobile network is since you could be just locked to Sprint or Verizon and this could be the reason why you get no signal.
If you made sure that your mobile operator was AT&T and you still have no signal in southeast – just wait till this is fixed. A lot of big carriers take advantage of using AT&T-based landline and once this company gets the issues they also suffer as well as their subscribers.
The service should be restored quickly since all the companies are interested in getting the signal back to their users. The problematic areas are Tennessee, Kentucky, Alabama and Indiana. Have you had any issues with the major carriers in these U.S. states or were you lucky to get no problems at all?