Hi onetime,

A GPS cell phone should be good enough as India generally has very good GSM network coverage in most towns and cities. 3G networks are being introduced in some major cities. Rural areas might be a bit patchy. If cost is not a issue then the Thuraya SG-2520 might be useful as it is a combined GSM/GPS/SAT Phone.

http://www.satphone.co.uk/networks/thuraya/handsetsnew.shtml

A rental Iridium Sat phone is a good idea but can generate unwanted attention when in use because of the rather large antenna.

You might find http://www.india-cellular.com/ useful for info on the current cell phone coverage situation in India.