Personal 3G/4G Devices in Schools

As a Technology Director in a technology savy district in Alabama, I am interested in how school districts across the country and internationally are handling the use of 3G/4G devices in schools. We currently have a WiFi network for school system owned devices and a Guest WiFi network for students, staff, and visitors who bring their own devices onto campus. We allow students to bring their personal devices including cell phones to school. In addition, we have addressed these devices in our AUP but although we do filter the access through our WiFi, we can not filter 3G/4G. We are looking into adding verbage to the Code of Conduct that specifically addresses personal devices on campus and also expectations for students and parents concerning devices with 3G/4G. Anyone with suggestions, please post your comments. I will be posting several articles addressing these devices.