Satellite Phones
Unless you’re in remote areas a lot, it pays to hire sat-phones. They are expensive and susceptible to water and vibration damage, and are also expensive in terms of call costs, so they aren’t an every day use item. Again, check who your carrier is before hiring or buying. One ... global ... company has access to so few satellites that a workable signal is rare and brief, which is not what you want in an emergency.
Put the sat-phone’s number on its case so that it is easy for everyone to find; emergency services will ask for it so they can contact you back. Similarly, if the phone has a security code this should also be attached to the case so there is no delay if it is needed in a hurry.