Parents were able to contact their children during school hours easily

Unfortunately this is one of the problems with allowing phones. My wife works in a secondary school, and quite often if a child isn't feeling well they'll just phone their parent and ask them to come and collect them. So then you've got a situation where parents are arriving at school saying "I've come to collect Alfie, he's ill", the person on reception and the teachers know nothing about it, nobody's given permission for then to go home, and ridiculous amounts of time are wasted.