Interesting, Bossman & akraus -- So the places where I CAN get AT&T coverage with this ostensibly Quad Band phone means that it is picking up the signal on GSM-1900?

It will be interesting to see what happens in Mexico--if wikipedia is to believed, Telcel uses 850 for 3g and hasn't rolled it out yet in the area where I'm headed.

So, theoretically, I guess, it should connect via GSM-1900.

Does anyone have any leads on reliable dual-sim quad-bands? I may try and do an exchange/return with focalprice.com if i have bad luck in Mexico.

I travel down there a lot, and many of the places I normally go around Mexico City are in Telcel 3g territory.

Suggestions for dual sim phones
 

Have had good luck with a dual sim quad band MFU V200 phone. Simple features, works well, very sturdy. Very basic though with a camera/video camera, MP3/MP4 player, FM stereo...no wifi, no alphanumeric keyboard, no TV, no touchscreen. But it does the job.

For a phone purchased from the US, lowest risk would probably be a Beyond E-Tech Duet dual sim phone. Only maker I'm aware of that has dual sim phones that are US FCC registered. You could also try before you buy at a store. Can be bought from several dealers including: Search Results for duet phone at JR.com They also have one of the lowest SAR ratings of any phone officially sold in the US: Other manufacturers cell phone radiation chart - CNET Reviews

In Mexico the 1900 band will work great. 3g is a newer techbology, so wherever the have 850-3g, they have 1900-2g.

Side note: you cannot call with the att SIM in Mexico to any place other than US/Canada/Mexico.

Yeah. Let us know how it works out for you in Mexico.

I actually also activated a couple of AT&T prepaid sims (one goPhone I bought for $1.25 on ebay and one regular AT&T sim I had laying around) for use when we go to Puerto Vallarta, Mexico, in a couple of weeks. Mainly for the $0.25 rate for incoming and outgoing calls. The goPhone sim will ONLY work in the phone I activated it on. I certainly do not anticipate any problems in Mexico since I will be using regular quadband/3G smartphones.