https://www.expat.com/en/forum/1103519-full-list-of-deltaairlines-customer-service-usa-contact-numbers-us.html
https://www.expat.com/en/forum/1103520-full-list-of-delta-airlines-customer-service-usa-contact-numbers-us.html
https://volleybox.net/fi/user/unitedairlines
https://www.expat.com/en/forum/1103521-ua-at-help-desk-deltaairlines-customer-service-toll-free.html
https://www.expat.com/en/forum/1103522-full-list-of-delta-airlines-support-toll-free-usa-contact-numbers.html
https://volleybox.net/fi/fanclubs/discussion/general-list-of-united-airlines-phone-numbers-in-the-usa-247-liveperson-the-ultimate-detailed-403902?new=true