Frontier Airlines ATL Terminal. At this terminal, Frontier Airlines customers can check in via airline counters or self-service kiosks. To ensure a smooth experience and to give time for security checks and check-in, it is recommended to arrive early. To enhance your journey, Terminal S offers a variety of shopping, dining, lounge, and other facilities. Check any of the many computer screens strewn across the airport to obtain the most up-to-date information regarding gates and flights. Have fun on your Frontier Airlines journey!