One phone kept blinking on my desk, and I could see on the display that the owner's boyfriend was sending her texts. I looked the boy's schedule up on our computer system and emailed the following to his teacher:
Please tell [name] to put away his phone. I’ve already taken [name]’s away so she’s not getting any more of his text messages.
The messages stopped.
Update, 12/6/10: Some schools confiscate phones for weeks. I'd have to wonder about that from a legal standpoint. I wouldn't wonder about the legality of suspending someone for habitually violating the rules, though.