Quote Originally Posted by barkerben
Looking through the data sheets, I might be able to get away with running eveything from 3.3v (which would make eveything very nice and simple. 3.3v regulators easy to get, everything running at same voltage)- it all depends on whether the GSM module (GR47 from erricson) can run at this level. It says 3.4v minimum, but it might work :-p

Ben
It's the ZX 4125 from Wonde Proud. It will operate up to....get this...3.6 volts! I am using one for a remote logging device. The input pins should not go above 3.3 volts. Slip a shottky diode in series with the PIC B+ line to drop it a bit for the I/Os. The GSM unit will be very finicky about voltage sags, so feed it well!