Indeed, although cellphones are officially banned in many suburban high schools in the New York area, on Sept. 11 they emerged in force. Carissa Kison, 17, who attends Passaic High School in New Jersey, slipped into the restroom to call her father, who works in the city, to make sure he was safe. ''My parents say it's good to have a cellphone on you,'' Ms. Kison said.