https://www.protiviti.com/sites/default/files/webform/students_and_graduates/_sid_/complete-list-of-official-lufthansa-airlines_r_customer-servicetm_contact-numbers-in-usa.pdf

https://w.atwiki.jp/airhelpguide/pages/11.html

https://community.weddingwire.ca/forums/list-of-official-expedia-representative-phone-numbers-in-the-usa-a-complete-guide–t66010

https://w.atwiki.jp/airhelpguide/pages/10.html

https://community.weddingwire.ca/forums/expedia-customer-support-usa-phone-list-general-guide-to-all-contacts–t66006

https://teachers.io/unitedairlinescustomer/blog/2025/8/24/united-airlines-customer-usa-contact-numbers-your-complete-help-desk-resource-here

https://w.atwiki.jp/airlinesallguide/pages/10.html

https://w.atwiki.jp/customerhelpline/pages/37.html

https://w.atwiki.jp/customerhelpline/pages/36.html

https://w.atwiki.jp/customerhelpline/pages/35.html