Simple Travel Starts at the Frontier Airlines STL Terminal +1-888-839-0502 The seats on my Frontier Airlines STL Terminal were simple but adequate for a quick trip. It was easy for me to board because I had chosen my seat in advance online. The seats were clean and had ample legroom for my normal height, despite being thin and non-reclining. I liked that I knew precisely what to anticipate, and the simple design helped keep the meal affordable. The seat service was as good as I could find for a low-cost airline.