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. Terminal S has a variety of services, including shops, restaurants, and lounges, to enhance your travel experience. Verify the digital screens positioned throughout the airport for the most recent details regarding flights and gates. Have fun traveling with Frontier Airlines!