Selling 2 of these for a friend (he won them in a contest).
This is the T&C he sent me:
Travel must end by 5/7/13, and it's best to book in advance because they allot only a limited number of seats on each plane for these travel vouchers. Sometimes they open up more seats when they see the plane is empty, so you can try then also.
How do you use the vouchers? Call 800-jetblue and ask to be transferred to crew support, then tell them the travel code with the pin # and they will check for availability. No, you cant check online.