In a message sent to Spirit customers Wednesday, Christie continued to point those four travel options from the airline, which he said "let you choose how you want to fly." Wednesday's announcement also noted plans to trade shares publicly again, although not immediately. Shares of Spirit previously issued by Spirit Airlines Inc. were canceled upon its exit from bankruptcy -- but it expects to re-list shares, newly-issued under new owners, "as soon as reasonably practicable." Meanwhile -- between wider economic turmoil, high-profile plane crashes and other consumer uncertainty -- major airlines have issued warnings in recent days about falling demand. Carriers like Delta, Southwest, American have all recently downgraded revenue outlooks for the first quarter.