Customer service is I believe Denver-based and generally very courteous. Frontier left our bags behind when I travelled DEN-PHX the day before Thanksgiving. One of our three checked bags made it. I am Summit Level and they put the priority tags on all three--lots of good that did. It took some time to find a rep to tell us they put them on a later United flight. I checked in about 50-55 minutes before my flight so perhaps the baggage hold was too full for my two roller bags. There were about 5 people on the flight missing bags. The flight was not even full.

I'm glad I don't normally need to do this for my business travel.