Cheap GSM module (SIM800) not connecting to the network

Using Arduino Project Guidance
36

It's not only about the Vcc power, pins need also a voltage divider. The serial port characteristic of the spec says 2.8 V max:

see p. 31 http://www.seeedstudio.com/wiki/images/4/46/SIM800L_Hardware_Design_V1.00.pdf