Frontier Airlines serves more than 50 destinations, including cities in the US, Costa Rica, Dominican Republic, and Mexico. True to its no-frills pedigree, the airline charges fees for most extras, including checked and carry-on bags, advance seat assignments, and airport check-in. Frontier doesn’t participate in any airline alliances, though it has several hotel partners, including Radisson, Wyndham, and Marriott. Members who provide their Early Returns membership info at participating hotels will earn award miles for their stay.