I've flown in many places with cellular service, and a few places with wifi available.
Last week, I flew a place called Waipi'o Valley on Hawaii. No cellular or wifi service at all. Sprint really lacks good service on the Big Island in general. I checked Verizon service on my dedicated to flying iPhone that has no contract and found no service for Verizon either. So much for calling my tracker with a Sprint Sim card!
I did not have a fly-away. I did meet a nice couple from Oregon who told me about a friend of theirs who had a Phantom fly-away. It got me thinking about the Find My Phantom App. would it work here? The answer is yes. Of course, all you can see is grid lines until you get cell or wifi service, but here are some screen shots I took afterwards.
i know we've had some great threads on trackers, but unless you have something like a Garmnin GPS tracker or a Marco-Polo type unit, Find My Phantom 2 Vision might be your only hope.