Amazon.com: Module,Development Board Module Kit,5~26V SIM Development Module,Fit for SIM900 850/900/1800/1900 MHz GPRS/GSM,Quad-Band 850/900/ 1800/1900 MHz - Would Work on GSM Networks : Electronics
SIM900 GSM GPRS Shield with Arduino Schematic Diagram | Random Nerd Tutorials | Arduino, Arduino projects, Electronics basics