Ok -I may in fact run most of the circuit off 3.3v, with the GSM off a seperate regulator, as the first section with just GPS and LCD is going to be ready first, and the system is modular.

3.6v seems a really annoying voltage - non standard and a pain to generate :-)
I could use a variable output voltage switching regulator, as you suggested.

Will look into it,

Cheers,

Ben