Not really according to the New York Times. It's mixed at best. And it doesn't make sense either. Bullies are more than capable of breaking the rules. The only thing that actually works here is that victims may not see the messages until after school. That's certainly not going to stop all of the other ways phones are used to coordinate bullying though. So now they get bullied all day still and taunted all night still.

The problem with cyber bullying is that there's no breaks in the bullying anymore. You used to be able to go home and relax before going back into it at school. So until schools actually go after bullies instead of supporting them against their victims this is useless.