I don't see anything wrong with it. I'd keep it simple. Introduce yourself, say how old your are, what year in HS, what position, and why you're interested in their school. Then see where it goes. Be ready to send a dvd or an email with a link to a video. You could ask about camps or other places that he could see you play.
He may ask you to go to their website and fill out the recruiting questionairre. It may not be a bad idea to do that before calling so you can show that you are already being pro-active.