Frontier Airlines ATL Terminal. Passengers using Frontier Airlines can check in at the airline’s counters in this terminal or at the self-service kiosks. It’s best to arrive early to guarantee a seamless experience, giving yourself enough time for security checks and check-in. A variety of facilities, such as shops, dining establishments, and lounges, are available at Terminal S to improve your travel experience. Make sure to check the airport’s digital displays for the most recent information on flights and gates. Have fun traveling with Frontier Airlines!