Its predecessor, Robert Mueller Airport, which was closed the day before Bergstrom opened, had the AUS designation for many years. Throughout the 1980s it was clear that Mueller had outgrown Austin's needs, and it's location in the city was a source of irritation to nearby residents.
After Bergstrom Air Force Base was closed and was converted to what is now Austin-Bergstrom International, which was opened in 1999. Bergstrom had the designator BSM until Mueller's final closure. This apparently still causes some minor navigational confusion, as of 2003.
Here is a list of airlines that serve Austin-Bergstrom International Airport: