Gordon W. Felt stood perfectly still, his head bowed slightly, as he listened to the frightened voices of three long-dead victims of Flight 93, their final words captured on answering machines just before the plane crashed into a reclaimed strip mine on the morning of Sept. 11, 2001. “That’s tough. That’s powerful,” Mr. Felt said, tears falling from his eyes during a visit to the new $26 million visitor center and museum that documents in wrenching detail the crash, which killed 40 passengers and crew members, including his brother Edward Porter Felt.