I purchased a dual sim, quad-band, FM, TV, PDA phone about 2 months ago. I also use AT&T for cellular service (in Indiana). Before buying I called AT&T tech support asking what frequency was used in the US, in my area and about traveling stateside & abroad. In the US AT&T operates on 850 & 1900 MHz. You can use a tri-band phone which would support the 1900 MHz or a quad-band with the 850 & 1900 MHz with AT&T as your service provider. Thus the quad-band phone will work anywhere & with most carriers in the US (AT&T, Cingular, Bell Mobility, Cellular One, Fido, Rogers, AT&T, SunCom, T-Mobile, TracFone). I have used the phone with mine & my husbands sim cards inserted at the same time & was able to use both cards & switch calls between both lines. There are many of these phones out there now. I took about 3 months pricing, comparing & evaluating before I finally purchased mine. On ebay you can find a number of these phones available now... but definitely DO YOUR RESEARCH! I ended up going with a company that has an office in Florida and offers a 2 YEAR WARRANTY ON THE PHONE!!! Almost unheard of. I know they honor the warranty because I had ordered an extra charger & for some reason it got to the point where it wouldn't charge the spare battery that came with my phone. I purchased the phone from ebay seller go2gold and their ebay store address is: http://stores.ebay.com/go2gold The model of phone I have that I can attest to working on AT&T with both sim cards is the 666B QUAD DUAL SIM Touch Screen PDA TV FM PHONE. The FM picks up loud & clear with station presets, the TV works fantastic and it has a ton of other features including a touch screen & the ability to handwrite on the screen. I paid $170 & about $17 to ship it.
Features of the phone are listed below:
Integrated 2.0 Mega pixel Camera with digital video & voice recording
Video & Music MP3, MP4
Long Standby Time 33 Days
Bluetooth 2.0 (Support Any Bluetooth, including A2DP)
WAP Browser (GPRS) Internet
SMS MMS message
Expandable Memory (1GB Micro SD card included)
Support up to 2 SIM cards
Support Bluetooth Handsfree
3D Dual stereo speakers
5 speakers 3-D Sound
+ Many Many MORE
This ebay seller has numerous dual sim, tri & quad-band phones available. On an ebay or any internet search you can find thousands of others. I'm happy with the purchase I made & with the fact that it has a 2 year warranty.
Good luck in your search & call AT&T to ask questions if you have them. I didn't let on that I was getting a phone made in hong kong because they want to sell THEIR phones. I asked the questions about what frequencies their service operated on & etc to make sure the phone would work. Obviously, they don't endorse nor can they advise you on the purchase of equipment they don't offer - and they would try to discourage you from doing so. I can tell you this... my husband has a friend who manages the AT&T store here in town & he took it in to show him after we got it. The guy freaked out cuz he thought the phone was so cool. Needless to say, he had us purchase one for him (I wouldn't tell him where I got it & he paid us a little bit above the selling price as a "finders fee" to get the phone).
After reading this post over it almost sounded like an advertisement for go2gold LOL it isn't. I personally do not know who they are. I've simply purchased 2 phones from them (one for me & one for our friend)& swapped out the faulty charger. I'm just one very happy customer & happened across your post as I was reviewing possible phones for my teenage & thought I could help you out a bit.
Good luck & have a great day...