Wow...that is a good question. Again, my experience is with Verizon, but I would think AT&T would be similar. I live west of Tampa, in Pinellas Co. Florida. Around here, there are franchise stores in every town. We have two Verizon corporate offices.....one in St. Petersburg, and one in Clearwater....each about 30 minute drive from me. (There may be one in Tarpon Springs as well.)

In my case, I had received an email from Verizon about reduced prices on iPhone, no contract, lower monthly fee, etc. I went to the nearest Verizon store. They said they could not honor/duplicate that offer.....turns out it was a franchise store. They told me I needed to go to the corporate store....and told me where to find them.

I would do an internet search for AT&T in your area. Pick up the phone and call. Ask questions. Ask for any "deals" or special offerings....and ask which locations honor them. For a very small additional monthly amount, I also have the insurance on the phone. I had one stolen....and the insurance company had a brand new (unopened box) iPhone 7+ at my door the next morning.

I would recommend that you visit an AT&T (Corporate) store. In my case, Verizon carried a variety of older models at much reduced prices....as well as the newest models. I chose the iPhone 7 plus and am happy with it. If you are on a limited budget, you may want to consider paying for your phone over time. In the case of Verizon, there wacs no interest charge....just extended monthly payments that they add to my bill. At the end of three years (in my case), I will own it and the monthly charges will disappear from bill.

I said 'corporate store' because the local Verizon stores are franchise locations....and can't begin to offer packages that the corporate locations can.

Good luck.