I'm a lurker but thought I'd share what I found today - hopefully it helps some people build better UAV's. I'm using cellular data too, but I am going the SSoftware2Mobile route. You can probably tell I kinda want to buy them anyways...

Someone on Ebay is selling 10 new Nokia GSM modules - the kind you can get direct AT and GPRS access to easily. For $10 each buy-it-now! Obviously they don't know what they have since it seems the store normally sells household items. They're 850/1900 which I think works for ATT/Tmobile, maybe more.

I found the datasheets and software docs here: http://www.control.com.sg/gsm_module.aspx
They need a SIM reader (see the hardware integration PDF pg 23, $2 part, easily ordered off Digikey or Mouser), power supply, and antenna ($10 at Sparkfun). The main connector is 0.05", also cheap at Digikey/Mouser and easy to manually solder.

Listing info:
NEW Nokia 12 Dual-Band Wireless M2M GSM Module 850/1900 (#170335219418)