Cellphones have the annoying habit of not working when you need them the most. In 98% of the places I hike or camp cellphones won't work.

Satellite phones are great, but they might be a bit pricey. I find a good radio to be the best solution. Find out which channel the local authorities are using.

Sometimes it's a good idea to have a daily schedule to report, if you are in really tough terrain. This allows the authorities to know where you are and start looking for you if you miss one of the scheduled calls.

Personal locator beacons, mirrors, whistles are all worth having around. Don't chose one of them, just carry them all in addition to a good radio.

Even if you manage to communicate, help won't always be on its way fast enough, specially if there is somebody wounded when a few minutes can mean the difference between life and death. You might want to look into a few good first aid and wilderness medical assistance courses.