Renee May calls
From 911myths
Renee May was a flight attendant on Flight 77. On 9/11 she called her mother from the plane to say that 6 hijackers had taken control, and everyone had been moved to the back of the plane. May provided her mother, Nancy May, with three phone numbers and asked her to call American Airlines. After the call ended Nancy May called two numbers, got an answer on the second, and relayed the information to Patty Carson, an American Airlines employee.
See: Carson's interview with the 9/11 Commission
Phone records
Unconnected call:
Successful call: