No, but it saves kids on an upturned car blocked in the sand by enabling them to ring for help (it has happened more than once where I spend my holidays in Greece) or in the middle of nowhere after having falling off their bicycle and are covered in blood (it has happened to me when I was 13 and believe me I wish mobiles were around then!).
It also helps us to help them improve their timekeeping by ringing them when late; starting early will get them into the habit of keeping in touch. In any case a mobile will not harm you child. Just put a very small & cheap one in their pocket (so that its outline does not show) and switch it in the vibrating only mode (there is no reason for all the world to know they have a mobile on them).
It is also allows communicating in text merry messages of the form "I will be a bit late" and the text reply "You are grounded!"
Having a mobile didn't save Milly Dowler.
The children have got to be street-wise, which means having their eyes and ears open and avoiding trouble. Walking facing on-coming traffic so you can't be kerb crawled and things like that.
At the moment if we go shopping in town we split into pairs and agree to meet at a key location like Waterstones or Druckers after an hour - hour and a half. It's a discipline sticking to meeting up like that; but it amazing how poor many people's timekeeping is now that they only have to text to say that they are going to be late.