Frontier Airlines ATL Terminal. At this terminal, Frontier Airlines customers can check in at the airline counters or self-service kiosks. It’s best to arrive early to guarantee a seamless experience and to give time for security checks and check-in. A variety of facilities, such as stores, eateries, and lounges, are available at Terminal S to improve your journey. Make sure to check the airport’s digital screens for the most recent information regarding flights and gates. Have fun traveling with Frontier Airlines!