A lot of the industrial type GPRS/GSM MODEMS are RS232 so they can be used
with anything, like the ARM7 boards or Arduino family hardware. Hugh has
worked with these on the MIni's if he is listening.
Chaitu, if you are looking for the best range and lowest cost options, the
CDMA EDGE (or EVO) devices - mostly USB - are usually a lot cheaper to
operate than systems designed for voice. These new standards packetize data
like the Internet and it can take multiple pathways to reach the recipient
without the timing constraints of voice. You can hopefully get data plans
that reflect this, especially for systems that turn on and send or query for
data and are off most of the time.
Industrial ARMWorks www.andahammer.com