Originally posted by bedhead
so it will fit? and with or without the case?

I've been on a LOT of planes in the past year, and on only one of them the overhead compartiments were big enough to store a guitar(with or without a case).
Your best bet is to keep it in a gig bag, and ask one of the flight attendants very nicely if they can put it away safely somewhere.

Here's some more info on the matter: http://www.win.net/~mainstring/carryon.html