GSM-GPRS Arduino SIM900 ( you can test it before buy )

From the shop's description

GSM-GPRS MODULE is an ultra compact and reliable wireless module. It is based on SIM900 4 Frequency GPRS module . The GSM-GPRS Shield is configured and controlled via its UART using simple AT commands. Module have two set power supply interface VCC5 5V power supply, VCC4 interface, 3.5--4.5V power supply, optional power on self starting (default) and control start. The MODULE allows you to achieve this via any of the three methods: Short Message Service, Audio and GPRS Features Fully compatible with Arduino uno and Mega. calling and message . SIM900 all pins breakout. Not just the UART port and debug port be layout. Not only can use the button for power on , but also can use the digital pin of Arduino to power on and reset the SIM900 module. Quad-Band 850/ 900/ 1800/ 1900 MHz Control via AT commands Supply voltage range : 3.7 … 5 V Size: 49mm x 47mm Package Includes GSM-GPRS Module V3.1 Quad band Antenna POWER CABLE