I got rid of ATT a little more than a year ago because the prices were simply too high. My wife and I were paying ~$110/mo for 2 dumb phones, texting on hers only, and a decent amount of minutes which we just about broke even on with the rollover. Too expensive for what we were getting, so we moved to our local CinBell for a year to save some money while we waited for wp8 (at that time Apollo) to arrive.
Finally wp8 did arrive, and I was all set to pay up front for the phones and do one of their prepaid plans. Then, after I thought it was all setteled I looked at ATT again and found their share everything plans.
It broke down to this:
TMo would have 2 HTC 8Xs, and unlimited everything with 4GB of high speed internet
ATT would have 2 Lumia 920s with wireless chargers, unlimited Talk and Text with 4GB of internet
The price difference after service and hardware? ATT was $200 more expensive over a 2 year period, with better cell service in my area, and with the phone I wanted (really the camera that I wanted). That $100/year was worth it for me.
Now I am approaching the 1 month mark and come to find that my wife and I have hardly used 300MB of data. Turns out we have wifi just about anywhere we go, so we will be able to knock our plan down to the 1GB/mo plan and save an extra $20/mo. So it turns out we are only going to be paying $20/mo more than we were paying when we had them 1 year ago... but with unlimited talk and text, and some pretty nice smartphones.
Not saying they are the best company on earth to deal with... but they are doing well because they are giving a fair deal.