Be very careful! A couple of years ago on my way to play in Chicago, I asked the clerk at the ticket counter if I was allowed to take my guitar on board. On being told that I could I proceeded to board. When I got to the the plane I was told I would have to gate check my instrument. I was carrying it in a gig bag( very well padded, I designed it myself). This happened on every flight! Including one where the plane's overhead bins were big enough to take the instrument. If they had told me otherwise, I had my Mark Leaf flight case out in the car, if they had told me in advance, I would have put my guitar in that. The worst part is that when I returned to my home airport, as we taxied to the terminal they announced that any baggage that had been gate checked could be picked up at the baggage carousel inside the terminal. Needless to say I threw a fit at the top fo the stairs! Fortunately, the pilot
on the out bound flight took pity on me and retrieved my custom made guitar before any damage could be done.
Just remember that whatever they tell you on the phone, or in person
it all comes down to what the onboard crew decrees. And they don't brook any arguments. Good luck, and next time take the train.

Mark Ross