I have a GSM shield based on a Sim300S.
when i look at the print i see that the 12V power is converted to 3.3v
and there is a max232 module on the board.

can i connect the 3.3 directly to my arduino. and drop my own max232 and the max232 on the gsm shield and connect the gsm shield directly to my serial pins of my arduino mega.

As I remember this module need power source in the range of 3.4 to 4.5 V but be careful it also need a current Burst 2A (not on all cases)

and Arduino provide 3.3v and 5v but the current not excess 1A