The GSM Shield connects your microcontroller to the internet using the GPRS wireless network. Just plug this module onto your development board, say arduino, plug in a SIM card from an operator offering GPRS coverage and follow a few simple instructions to start controlling your world through the internet.
You can also make/receive voice calls (you will need an external speaker and microphone circuit) and send/receive SMS messages.
As always with Arduino, every element of the platform – hardware, software and documentation – is freely available and open-source. This means you can learn exactly how it’s made and use its design as the starting point for your own circuits. Hundreds of thousands of Arduino boards are already fueling people’s creativity all over the world, everyday.