SIM900 GSM/GPRS shield is based on Quad-Band SIM900 GSM/GPRS module. It provides Arduino with GSM/GPRS function.
This shield allows you to make voice calls, send SMS or make connections to the Internet network.
On the shield, there is a serial port toggle switch for you to select either software serial port or hardware serial port to be connected to GPRS Shield.
If you choose software serial port, you need to use the Software UART; otherwise, you need to use the Hardware UART.
The shield includes a high capacitor dedicated to RTC (Real Time Clock).
If you toggle the switch to DBG-Port, you can connect the port to Arduino or connect the port to PC by Arduino to proceed the debugging.
1. Auto-adaption to 3.3V and 5V main board, supporting 3.3V platforms such as leaf maple and Chip kit;
2. After connecting the SIM900 shield to Arduino, 9V/2A DC power supply is needed. Otherwise, there might be malfunction;
3. Quad-Band GSM/GPRS 850/900/1800/1900MHz (Support 2G card of UNICOM, China Mobile, do not support Telecom card).
We use SIM900 GSM Module – supporting communication in 900MHz band.
You should check the mobile network band in your area.
More information: here