For travel around Australia, where cell-phone coverage is woeful, I like to use a Garmin inReach device. It communicates with satellites and so is always available, even in the event of natural disasters.
For a monthly subscription you can use it to send and receive text messages (not voice or images). It has an iPhone app that shows your position on a topographic map (great for hiking) and a feature called Mapshare where your family and friends can follow your progress via a password-protected web page. This includes tracking the journey.
It also has an SOS button that connects the user, via satellite, with a Garmin service that can alert emergency services.
It is relatively expensive but is worth considering for peace-of mind.