http://ia600806.us.archive.org/31/items/usa-airlines-hub/Official-list-of-United-Airlines-CUSTOMER-service.pdf
http://ia902900.us.archive.org/30/items/us-united-airlines/Official-Directory-of-United-Airlines-CUSTOMER-service.pdf
http://ia600906.us.archive.org/35/items/usa-united-travelhub/Full_List_of_United_Airlines_Customer_Service_Numbers_Guide.pdf
http://ia902807.us.archive.org/1/items/us-united-guide/US_United_Airlines-Tm-Official-Customer-Service-Numbers-Quick-Guide.pdf