Here's the rundown on the Android phone I just bought and am using today on my AT&T line.
Model: Samsung Google Nexus S i9020A
This is the specific model number for the phone that runs on AT&T's frequencies.
I bought mine here:
Samsung Google Nexus S i9020A 850/1900 3G (Unlocked) (Black)
Here are specs:
Nexus S ? The new Android phone from Google
More detailed specs:
Samsung Google Nexus S i9020A - Full phone specifications
I simply cannot say enough good things about this phone.
Yes, it's very expensive unsubsidized, I paid just under $600.
But it's also unlocked and rooted, therefore I can use it without any limitations. In addition I'm not under contract with AT&T either.
The "Pure Android" experience is unlike any other. I can easily see myself using the phone for two years. Android is not optimized, nor does it take advantage of dual core processors yet.
Therefore a dual core phone is a waste at the present time. The chip makers simply pushed the chips out because they're in the business of selling their latest product.
If you can wait I have it on good authority that AT&T will be selling it from their stores in the near future.
It's setup so that the carriers cannot molest this phone with their bloatware so the phone you buy from AT&T will be the same phone I've just purchased. The only question I cannot answer is if it will be unlocked.
Either way the Nexus S is the phone to have, based on my personal experience.
Cheers