SIM900A – GSM GPRS Module

GSM
module is used to establish communication between a computer and a GSM
system. GSM module consists of a GSM modem assembled together with power
supply circuit and communication interfaces (like RS-232, USB, etc) for
computer. The MODEM is the soul of such modules.

Features:

• Standard serial RS232 interface 
• Serial TTL interface for direct interface to microcontrollers
• Power, Status and Network LEDs for easy debugging
• Onboard MIC/Speaker circuits and 3.5mm audio connectors.
• Standard AT commands
• Comes
  with an onboard wire antenna for better reception. Board provides an
  option for adding an external antenna through an SMA connector
• Adjustable serial baudrate from 1200 to 115200 bps