Balance world Inc SIM900 Quad-band GSM/GPRS Shield for Arduino UNO/MEGA/Leonardo Based on SIMCom's SIM900 Module Quad-Band 850 / 900/ 1800 / 1900 MHz - would work on GSM networks in all countries across the world. Control via AT commands - Standard Commands: GSM 07.07 & 07.05 | Enhanced Commands: SIMCOM AT Commands. Embedded TCP/UDP stack - allows you to upload data to a web server. 12 GPIOs, 2 PWMs and an ADC (all 2.8 volt logic) - to augment your Arduino.