16 Year-Old Talking With 25 Year-Old - Can It Be Stopped?

I'm from Florida, and my husbands daughter will be 16 in three months. The guy that she's talking to will be 25 in two months. They both say they have never been involved in sexual activity together, and are not seeing each other. Just talking on the phone. The cell phone number that is under his name is on his daughters phone bill over and over again. If he has no proof that they have had sexual activity, and are just talking, can he do anything about this?

He can seek to get a protective order but without evidence of threat it might be tough

You can go to the phone company and have his number blocked and put a password on the account otherwise the daughter could just call and have it unblocked.