I dont know that I can prove this, but Im pretty sure that AT&T was throttling my "unlimited" data plan well below the 2GB limit. It was bad enough that I rarely used more than 1GB of data per month.
Fast forward to my iPhone 5 upgrade. Granted there is decent LTE coverage here in Houston, but with no change in my usage habits I hit the 90% mark of the 4GB plan(I needed tethering, so I had to "upgrade") 18 days into the billing cycle. My main data consumption was iTunes match over cellular. I was getting constant buffer underruns with my iPhone 4 on 3g, but now Im hitting the data wall halfway through the billing cycle. Its now in AT&Ts best interest to open the pipe for me so I can pay overage fees.
I dont know that it would be better on a different carrier, but I certainly harbor no goodwill towards AT&T. I feel like Im one hassle away from buying out my contract.
Just getting my iPhone 5 proved to be a multi hour headache due to an AT&T agents royal screwup of my initial upgrade. I ordered a 64GB black phone, was shipped white. He also updated my home/billing address incorrectly(more on that later) I returned it, and they spent 2 hours reversing the upgrade and giving me a new sim for my iPhone 4. That took so long that I couldnt re-order the upgrade. A week later I used the AT&T website to order the new phone, however, it could only be shipped to the billing address that the AT&T agent mistyped when I originally ordered the phone. So I had to cancel the order. But it wasnt that simple. I am a "premier" account and premier support isnt open on weekends. I had to go to an AT&T store and cancel the order. Then I had to call premier support on monday and reverse the upgrade. The next weekend, they finally had some black 64GB iPhones in stock. I bought one. Guess what? it had an intermittent power button. I had to set up an appt with an apple store to get that fixed. Fortunately the Apple store experience was much better. So 3 iPhones later, I have an iPhone 5 with a bad carrier and have to now worry about my data usage. First world problems I suppose.