IT in the hills..... Pah!
Nothin' buggers up a bit of IT kit better than a bit of moisture.
Personally, I rely on map & compass but I do stick the mobile (turned off & in a waterproof bag) into the rucksack as a backup.
In the car (vehicle based expedition....), although the GPS will be the main navigation device, I will still carry the map & compass as the GPS will be worse than useless if I manage to submerge it. (I've been know to drive the car while being waist deep in water!!!) However, current position and the days route will then be transfered to paper every evening.
In other words, IT kit is nice but at times of emergency you need some thing that's fail safe.
M