Short version: Power it off immediately and put it in a bag of uncooked rice. Long version is here (http://www.ifixyouri.com/blog/?p=412)
iPhone water damage - steps to take if it happens to you (http://www.youtube.com/watch?v=eg8Fpb3UjHY&feature=player_embedded#normal)
Hope this video might save a few iPhones out there.