I booked with them last year and called about changing my fare and was told I would have to pay the fee, which was more than the savings. So far the only 2 that I know that will give you the price difference is SW and JB. However, on Airtran last year, they cancelled my flight and put me on a connecting flight which I did not want and I called and they did refund me the entire price of my tickets -- then I purchased my return flight on Jetblue. (I had gotten a great price on Airtran and had used the coupons, but I just didn't want to do a connecting flight when my flight is only 2 hours non-stop.)