Chances are your business trips are packed with important meetings, deadlines, and set-in-stone plans. So when airlines throw extra fees your way, you typically just take it and pay them, because you don't have any other choice. 

But some of those fees can really put a dent in your pocketbook. In a new survey, USA Today got the lowdown from a dozen U.S. airlines about fees they charged in 2013. Here are some of the more surprising takeaways that you might want to keep in mind before booking your next trip: 

  • Delta Air Lines charges $400 to change a ticket on some international flights.
  • On some international flights, United Airlines and Hawaiian Airlines charge passengers with overweight bags (71 to 100 pounds) a $400 fee, while American Airlines charges $450.
  • When it comes to checked bag fees, the most expensive airlines are Spirit Airlines and Allegiant Air. They charge $100 and $75, respectively, for bags checked at the gate. Both airlines charge much lower fees for bags checked ahead of time and online.
  • Most of the airlines surveyed charge extra for booking frequent-flier award tickets over the phone, according to USA Today. Spirit charges passengers $25 for booking flights over the phone, and an additional $100 if a passenger is booking the flight within six days of departure. US Airways charges passengers $90 to book an award ticket for an international flight on the phone.

All those fees add up to huge revenues for the airlines. The Department of Transportation found that U.S. airlines reported $2.6 billion in baggage fee revenues and $2.1 billion for flight change fees during the first three quarters of 2013, according to USA Today.