Carry at least one mobile phone, or satellite by group, as well as emergency numbers. Although it takes off, a phone can be used in an emergency. Satellite phones have the advantage of having coverage in places where cell phones are not the absence of nearby antennas, and capturing its coverage of communications satellites like the GPS.
In addition, mobile phones for emergency contact participants in the activity if necessary, you should also have walkie-talkies for communication between the guides or guardians of the exit (if any) or members of small groups so economic and real-time. In this case communications must conform to the rules of radio communication.