Gabriel,

I do not know USA, but rest of the world uses GSM-phones which are
available in many different forms
for OEM needs.

I use PIC +Nokia PC card II ( max. 44kbsp speed).
It is basically PCMCIA format GSM-phone with integral antenna. Add 5V
and PIC + program.
Very easy. I have done interactive Coca-Cola vending machines with
Nokia's PC CARD II.

Pekka 

-- 
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Pekka Ritamaki, Probyte Oy Microprocessor software & hardware design
Nirvankatu 31, 33820 TAMPERE, FINLAND http://www.sci.fi/~pri
tel: Int. 358-3-2661885 fax: Int. +358-3-2661886 email:pri@sci.fi