I considered the SIM800 that is 3.5 to 4.5V and the SIM 900 that is 5V.
I ended on the second.
Anyway it really consume energy, it is possible to put it insto a sleep mode but i prefer to close totally his energy line and reset it all the time, together with his dedicated 328.
Do you think that just a voltage divider would not be enough? I also saw solution with just just a resistor in series like this.