What is a GSM Modem?

A GSM Modem modulates outgoing digital signals from a computer or other digital device to signals for a GSM network and demodulates the incoming GSM signal and converts it to a digital signal for the computer or other digital device.

Strictly speaking a GSM Modem can be considered as a GSM phone without the conventional keypad and display and that it is not battery operated as the conventional GSM phone. However, most GSM phones of today have the modem functionality inbuilt into them which allows them to be interfaced with a PC and to be used as a GSM Modem.

A PC or any other digital device uses AT Commands to interact with a GSM modem. AT Commands allow a host of functions to be performed viz sending/receiving SMS, Making a voice call, Accepting a incoming voice call, Modem configuration etc.