Can anybody provide an answer on carrying a musical instrument with Cape Air or InterCaribbean?

I travel with a guitar -- its a Martin Junior Dreadnought (for those who may want to know) but it is 3/4 the size of a 'regular' guitar. On the larger airline jets, I can carry it on and stow it above the seat. On the smaller commuter/regional jets, I carry it to the plane and store in the hold and I pick it up at the side of the plane when I arrive. I never check it as a piece of luggage (I always fly carry on only for my BVI sailing trips)

What I am wondering about is: if I look at Cape Air or Intercaribbean as the final leg of my trip to EIS next February, do their planes (Cessena 402 for CA/Twin Otters for IC) allow me to have it on board (though stored with all the other luggage)? Or do I have to buy a seat for a guitar (not in my budget!)?

With Seabourne, I carried it to the plane and they stored it for me and I picked it up at the tarmac at EIS. When arriving at STT on the major airlines' 737 or 767s, I had it with me in the cabin.

Thanks,

Donald