FWIW, in some areas, ATT has re-farmed (=carved out/eliminated) part of their available GSM spectrum for 3G/4G. So it's possible that you may receive less than ideal service with a handset than does not include the 3G frequency bands. For ATT right now, you should have a handset that includes UMTS 850 & 1900. The old trusty quad-band GSM handset is more useful in some ways for international travel than it is in the US.
Considering this phone is generally a poor performer if you read the reviews @ Amazon, and the fact that it comes in at least two flavors, one of which does *not* include the bands you need for North America, you might consider looking around for something else, even if it means spending a little more.
The good thing is Amazon has decent return policies though. In that sense it's not a huge deal. Just test it out thoroughly the first couple weeks you get it.