Frontier Airlines ATL Terminal. Customers of Frontier Airlines can check in at the 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 advisable to arrive early. To make your trip better, Terminal S offers a range of amenities like shops, restaurants, and lounges. For the most up-to-date information about flights and gates, be sure to consult the digital screens located around the airport. Enjoy your journey with Frontier Airlines!