If you push this hard enough, the school board will simply ban cell phones from students altogether.
Ive done a little research on this, and apparently its different from state to state and even from one school district to another as far as cell phone rules, but from what Ive read many states even allow teachers to look through content on the phone if they have 'suspicion' evidence of wrong-doing exists on it. So to the OP, if I was you, Id be happy your school's rules are as lenient as they are.