Ozeki GPRS Module
You can use the Ozeki GPRS Module to send and receive SMS messages. The SIM900 is used for GPRS communication, which is soldered directly to the board. You can use it by inserting a SIM card and controlling the SIM900 with AT commands.
It has an ATmega328P chip integrated, so you can program the Ozeki GPRS Module by using the Arduino IDE environment. A reset button can also be found on this module. The module connects to PC via an USB to serial converter chip (CH340G).
Pinout of the Ozeki GPRS Module:
Figure 2 - The pinout of the Ozeki GPRS Module
An example code that connects your PC to the SIM900
The role of this code is to build a communication stream between your serial port and the SIM900 chip. Through this communication stream you can send AT commands to the SIM900 modul. For example the simplest command is AT\n and the response should be AT\nOK\n
SoftwareSerial.h is a default library connected to the Arduino IDE, so you do not have to do anything to acquire it.