If you have a newer iPhone you should be able to use Satellite communications if you get into a jam off grid. Also, again for emergencies, when calling 911 it doesn’t matter what network your are on, most modern phones will connect to any available network to complete the emergency call. If you are really worried about it you can also add T-Mobile’s Satellite feature to your phone (not changing service providers, but just adding this coverage option) and that would give you texting coverage as well as emergency services contact.