I think a basic system is presently used by at least one of the UK police air support units so that the phone can be heard above the aircraft interior noise. We don't, but have used mobile phones indirectly to locate lost persons by having them talk direct to our unit by phone and info then relayed on police R/T. Obviously this would be insufficient over longer ranges. I would always recommend a 'phone to be taken asa survival aid if out anywhere in the more remote UK areas.
There may be technical problems in getting the ground phone to "log on" if outside normal network coverage.
Anyone know more?