In this I would like to share experience with a cheep SIM800L GSM module that I purchased from my local supplier. This is a very nice and useful module that supports GSM/GPRS using 2G spectrum. You can also make calls and send SMSs using either AT commands or using Adafruit FONA library. You can download the FONA library from github page. Connection is very simple and a basic sketch uses only TX , RX, and RST pin. This module is designed to power somewhere between 3.7 to 4.8 volts but I powered up with 5 Volts external supply. Initially I tried to give power from my Arduino UNO 5 Volt pin. It initialized, but soon I got to know that my SIM is not getting registered in network. A quick googling gives me the answer that I would need a external power source as Arduino 5 Volts pin does not have enough power so that SIM get registered. It consumes a good amount of current for network search and registration. Also I also connected my modules GND pin to Arduino GND pin