I'm not an expert, by any stretch of the imagination. but from my reading...placing the phone into "airplane mode" will stop the wasted energy of scearching for phone and wifi connections. And shut off the "track" feature of the apt.. I think at this point my only stumbling block is, "energy usage". I think to be practical, I'll be forced to carry some form of power storage.( plugin power cube and cord to the storage soulation, included). looking over amazon there's WAY TOO many! to blindly chose from. I think I'll have to experiment by taking the plunge and buy the g.hook's program for the PTC....and turn the phone on and use it as I would in the field (15 requests for position a day should get me a basic coumpssumtion number)...after a day or three recheck power used and only then I'll have a power per day number I'd be willing/need to carry. I can always fall back on my gps, but frankly that's been getting progressively harder and harder to read-even with readers. The brite, big screen of the smart phone along with the ability to view terrain ahead in profile, will be a welcomed change.