a friend of mine is only getting text messages from other iphone users and no messages from non iphone users. i ran down the settings in notifacations and messages. we are setup exactly the same. i get messages from non iphone users, though.
Another thing to check is he could only be getting "imessages" and not text messages at all. Tell him to make sure his text message plan didnt get removed from his account. I have at&t and it has happened to me on a new phone purchase once.