A cell phone was basically considered a required item like binders and pens at my kids' school. Rather than ban them, they try to encourage appropriate use.

For example, they encourage the use of the calendar app for tracking assignments and test dates. They use the camera to capture information for homework. Kids have projects that sometimes involves recording audio or shooting video. There's also a twitter-like app that the teacher can use to broadcast to students and students can use to communicate with the teacher.