Its embedded into GSM modules; Phones need it to do anything, to check firmware versions, to send and retreive SMS messages, to make calls etc. I used it to con

Its embedded into GSM modules; Phones need it to do anything, to check firmware versions, to send and retreive SMS messages, to make calls etc. I used it to control the 3G dongle I had (basically, a GSM module in a stick). Most times the device will act as a serial device.