You can only pay before you leave for the trip to Orlando and then must go through BAGS to pay before you check-out. We did this in Aug. and it is so easy. Check to see if Air-Tran lets you pay for your luggage on-line. Delta let us do it when we printed our boarding passes 24 hours before our trip. Also, check to see, some of the airlines are charging more to pay for luggage at the airport than doing it on-line. Using BAGs at the resorts is so easy. As the pp said, you call the number (free on Disney phones) the day before you check out. Just have your flight info (or confirmation no.), credit card, and pen/paper handy. Just follow the reps instructions, write down the confirmation number and then take it the day you check-out to the airline desk at the resort and they do the rest. They will check the confirmation number, take your bags and print boarding passes for you.