How do you ask someone to prom who lives in a different state?

I wouldn't get too fancy about this. College means lots of studying and hard work, so if you want him to go to the prom with you, then you have two choices ... phoning him and asking him (his schedule may be tight) or, going there for a surprise visit, but if you do don't expect him to spend every waking moment with you because he's probably tired from studying. You may get a dinner or some time alone together if lucky. Hope he can make your prom!