I never said it had to be a smartphone, I had a Nokia throughout school and only got a smartphone last year (aged 21) as a work requirement. In an urban environment where everyone can travel by buses or tube which run at least at a 5-10 minute frequency, there is less to be concerned about perhaps. Anywhere else though, there are no doubt parents who would refuse to allow their children to be proactive and participate in those extra-curricular activities because of the problem if something goes wrong. Obviously they haven't always been 'essential', but in the past having some change for a payphone probably was for most. The world has changed and, while I do love environments without mobile phones, I'd personally see it as irresponsible to deprive someone of a way out in an emergency because of it.
I think what I'm getting at is for 90%+ people at 90%+ schools, a 'no mobile' policy probably works quite well - there are sufficient backups along the way (public transport and well-lit streets with reputable shops, all of which can provide support) from home to school and back that not having a mobile will not prove a problem, and will improve the quality of conversation / reduce theft, you name it. There are lots of pros. But there will be those who lose out, disproportionally those less fortunate, being those who may have to travel further on less frequent transport in less secure areas. Not being allowed a phone for that peace of mind may well be something holding them back.
It's not on topic and I promise not to message again (at least on this forum!) about it, but I think it is useful food for thought.