What really bugs me is their response to the Consumerist. A very simple question was asked, and they kept dodging it. Frontier Now Offering Confusing Range Of Carry-On Fees If You Don’t Book Through Its Site

Since it's not mentioned above, the carry-on fee only applies if you booked outside of Frontier's website (Expedia or what have you) and the fee could also be as low as $25 if you encounter it. Wonder if they'd charge it to pax originally booked on another airline, then rebooked to F9 due to irrops or something?