This has been circulating around the Internet lately:
“If you have ever been lost while hiking or stranded with a broken-down car, etc… and you notice your mobile phone is either low on juice or has no signal, here is a tip that very well may save your life. Change the voicemail on your phone to a message that gives your approximate location, the time, the date, your situation (lost, out of petrol, car broken down, injured etc…) and any special instructions such as your are staying with the car, you are walking toward a town etc. The best part of this is that even if your mobile phone dies or stops working, voicemail still works, so anyone calling your phone looking for you will hear the message and know where to find you or where to send help.”
The major problem with this is that you can’t change the voice mail, or anything else when you have no signal. Nothing will leave the phone without connection to a site, so you my as well use the battery to start a fire.
In addition to being a passive communication requiring someone to call you to get the information, changing the voice mail will use more power than other forms of messaging. If you have the power to change your voice mail, you may as well make a phone call and get help started on the way. Otherwise you can use email or text messaging to send out your information. Without graphics or pictures it takes much less power and signal to send text than to send voice. Also, a text message will wait until you find the cellular signal before the message is sent making the chances that the text will get through to the destination more likely to happen.
If you know you are going in to areas that don’t have cell phone coverage, consider having an alternate means of communications such as FRS radio, CB radio or amateur radio