Adormi gsm/gprs shield for arduino and based on the sim900 quad-band gsm/gprs module. It is controlled via at commands (gsm 07.07, 07.05 and simcom enhanced at commands), and fully compatible with arduino. The adormi gsm shield connects your arduino to the internet using the gprs wireless network. Just plug this module onto your arduino board, 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.