FRONTIER AIRLINES announced last month that it would begin charging passengers for carry-on bags. It isn't the first to do this—Spirit Airlines, a much-moaned-about ultra-low-cost airline, also charges for cabin baggage.RONTIER AIRLINES announced last month that it would begin charging passengers for carry-on bags. It isn't the first to do this—Spirit Airlines, a much-moaned-about ultra-low-cost airline, also charges for cabin baggage.