Here's a similar question/answer about the PDA! The PDA can be opened and I guess Natsume can install a tiny bomb or something inside of it... Once somebody regains a computer, it may be possible to unlock more of what's there!

Nope, students get only one school issued PDA and they must keep track of it for all three years. It isn't strictly necessary to have/use it, so if they get lost or broken, it's a lesson to the student to take better care of their things.