My old High School prohibited cell phone usage during school hours. It was to be turned off throughout the course of the day, and if it was needed it was only to be used out side the building.
If a student was caught using a cellphone it would be taken away for 24 hours on the first offense, 72 hours on the next offense, and one full week on the third offense. Cell phone usage distracts the student from learning (which is proven). Additionally, it is incredibly rude (in my opinion) to use a cell phone while someone is trying to talk to you.
I wouldnt want it done to me, and I am sure people wouldnt want me to do it to them. Furthermore, it upholds a certain amount of decorum in the classroom setting which allows students to have maximum growth, and it doesnt hinder possible potential from the certain student.
I am happy they didnt let me use my cellphone during school hours, because now all I see is teens divulged in their blackberries and iPhones, and have lost a large aspect of what it means to communicate with other people.