The Arduino GSM Shield allows an Arduino board to connect to the internet, make/receive voice calls and send/receive SMS messages. The shield uses a radio modem M10 by Quectel. It is possible to communicate with the board using AT commands. The GSM library has a large number of methods for communication with the shield.
The shield uses digital pins 2 and 3 for software serial communication with the M10. Pin 2 is connected to the M10’s TX pin and pin 3 to its RX pin. See these notes for working with an Arduino Mega, Mega ADK, or Leonardo. The modem's PWRKEY pin is connected to Arduino pin 7.
The M10 is a Quad-band GSM/GPRS modem that works at frequencies GSM850MHz, GSM900MHz, DCS1800MHz and PCS1900MHz. It supports TCP/UDP and HTTP protocols through a GPRS connection. GPRS data downlink and uplink transfer speed maximum is 85.6 kbps.
To interface with the cellular network, the board requires a SIM card provided by a network operator. The most recent revision of the board uses the 1.0 pinout on rev 3 of the Arduino Uno board.