There are a ton of phone apps that run on cellular data. But that means you must have cellular data. If you want a tracker that tracks everywhere, you will need to get a satellite tracker as they, of course, use satellites instead of cellular. Since the companies (Garmin and Spot) do not own the satellites, they buy the time/data from the satellite owners and thus pass on the costs in the form of a subscription.

If you stick with the phone apps, check your carrier's coverage area as the app is only as good as the coverage. I "think" Verizon is the "best" in rural America but it too will lack coverage in numerous areas.

I will be interested to see if there are others other than Garmin and Spot.