Frontier Airlines ATL Terminal. Customers of Frontier Airlines can check in at airline counters or self-service kiosks at this terminal. To ensure a smooth experience and to provide time for security inspections and check-in, it is recommended to arrive early. To enhance your travels, Terminal S offers a variety of amenities such as dining options, retail stores, and relaxation areas. Check the numerous digital screens located throughout the airport to obtain the most up-to-date information regarding gates and flights. Enjoy your vacation with Frontier Airlines!