Mobile phones have, without doubt, contributed to saving people's lives in the mountain environment. However they have also been misused and abused and led to much time-wasting for voluntary mountain rescue teams.
If you're taking your phone with you for emergencies, then make sure it's fully charged. If it's a smart phone, and you spend the day using its features, then it is quite likely it won't have enough battery power to use it later in the day in an emergency. Be careful if using apps for navigation. Full mapping software is available, but the stuff like Google maps doesn't provide anywhere near enough detail to navigate by.
Quote from British Mountaineering Council:
"This is not a safety device, nor does it guarantee the delivery of any perceived or needed services in the mountains. Use of a mobile phone in the mountains, in a non emergency situation, may be an infringement on the mountain experiences that others have come to enjoy and an intrusion into the wilderness experience. Using a mobile phone to
- Ask for directions,
- Ask for additional food and clothing to be brought to the user,
- Ask to be rescued for a non life threatening or disabling injury,
is properly considered by those agencies who might be called upon to render such assistance as an abuse of the technology, both on a practical and philosophical level. A cellular phone is a communication device that may be aid in the saving of lives and limbs if used solely for that purpose in the mountain environment, after all the above have been taken into careful consideration."