Ideally, students should be able have phones and control their own usage. Unfortunately, the temptation is too much for most students. It's a constant battle to keep the phones out of sight with the ringer turned off. Phones have become major disruptions in most classrooms.
Surprisingly, some of the biggest offenders of cell phone use in school are the kids' parents. You would not believe how many parents insist that their children answer their phones even if they are in the middle of class. My students have actually been punished if they didn't answer phones when their parent called. I have been cursed out by parents when they find out that I wouldn't allow their child to answer the phone during class. Some of these parents are the same ones who are up in arms about poor student behavior and poor student performance in schools. They don't seem to realize that they are a big part of the problem.
I'm sorry to say that I hate the fact that students are allowed to have cell phones at my school. I say that every teacher should have a phone, but students should not be allowed to bring them onto the property.
As far as students who stay after hours, parents should have a prearranged time to pick up their children at school and show up on time to pick them up.