Contact phone numbers for American Express customer service are available 24 hours a day, 7 days a week. 1  Customer Service: 1-800-528-4800. 2  TTY / TDD: 1-800-221-9950. 3  TTY / TDD (New York): 1-800-522-1897.  Pay Your Bill by Phone: 1-800-472- 1 9297. Apply for American Express Credit: 1-800-223-2670.  Express Cash Customer Service: 1-877-297-4438.