Sim900/sim900A Mini Module With Arduino UNO The Arduino IDE includes a library for their GSM shield using the Quectel M10 GSM chip, and Surprise! it is almost identical to the Sim900A chip!
SIM900 library for Arduino Uno & Pro min - Programming Questions - Arduino Forum
Arduino uno + gsm shield sim 900 problem - Arduino GSM Shield - Arduino Forum
SIM900 GSM GPRS Shield with Arduino | Random Nerd Tutorials
How to Send, Receive and Delete SMS with IOT Devices (Arduino and GSM Shield) - CodeProject
sim900 library - Arduino GSM Shield - Arduino Forum