It’s really not so hard to to control cellphone use. If you don’t pay for internet and texting and your kids use them, it shows up on the bill; if they overuse their allotted minutes (and by the way, you as the parent can choose to pay for a limited number of those minutes)it shows up on the bill. Like credit card and bank statements, simply reading every item on the bill can alert you to misuse, and you can take the necessary action, such as taking away the phone. Our rule at home: when a child is old enough to travel around without an adult, they may have a phone; no texting, no internet, and limited minutes; phone is turned off and put away when at home.
Also, here in E”Y, terrorism is r”l a constant worry (and I hear that it ought to be more of a worry in the U.S. than it is). I want to be able to get in touch with my children in the event of an attack ch”v, without having to try and get through to a Yeshiva or B.Y’s phone system that is crashing from the volume of the calls.