1.0 Problems using the sim800
I am often asked "Why doesn't my sim800 connect?" The reason most beginners have is that they have connected the sim800 supply to the Arduino 3.3V supply
This will not work as the sim800 requires at least 2A to boot up, and must be supplied from a more robust supply capable of delivering 2A.
A work-around is to use a weaker supply - maybe 1A and then connect a large cap (4700uF) directly to the sim800 3V3 pin.