SIM900A Modem is built with Dual Band GSM/GPRS based SIM900A modem from SIMCOM. It works on frequencies 900/ 1800 MHz. SIM900A can search these two bands automatically. The frequency bands can also be set by AT Commands. The baud rate is configurable from 1200-115200 through AT command. The GSM/GPRS Modem is having internal TCP/IP stack to enable you to connect with internet via GPRS. SIM900A is an ultra compact and reliable wireless module. This is a complete GSM/GPRS module in a SMT type and designed with a very powerful single-chip processor integrating AMR926EJ-S core, allowing you to benefit from small dimensions and cost-effective solutions.

Approved GSM Module Link:

Instructable Tutorial: 
https://www.instructables.com/GSM-SIM900A-With-Arduino/

SIM900A key features:

GSM SIM900A Functional Diagram:

The above figure shows a functional diagram of the SIM900A and illustrates the mainly functional parts:

• The GSM baseband engine
• Flash and SRAM
• The GSM radio frequency part
• The antenna interface
• The Other interfaces

Package Includes:

• 1x sim900a gsm module
• 1x antenna
• 1x power cable