If you're an ATT customer already and have been for a while, you should call ATT customer service (Option #7) and negotiate with them. I have been with ATT over 12 years and they waived the upgrade activation fee and gave me a credit for the full amount of the CA sales tax to my service plan AND sold me the sexy garnet red phone for $50 for my single line account.
If you tell them Amazon will negotiate a similar deal they'll do something for you (though Amazon cannot waive the activation fee). And also remember that when buying a phone from a third party if you want your existing plan grandfathered (I had unlimited data and 200/text msg plan), there's no guarantees it will happen right away. When you buy from ATT it's grandfathered over instantly.
Also when you buy a phone from them when you call, there is no restocking fee if you return the phone, which you can't get when buying the phone in a corp ATT store. As you may know already, Amazon has an additional Early Termination Fee if you cancel your service contract within the first 6 months on top of ATT's ETF. Buyer beware