Shocking Voice Identity Reveal

Alice is talking to a stranger on the bus, when she realizes that she's heard his voice before, somewhere. Moments later, Alice realizes she's talking to Bob, her Mentor whom she hasn't seen in 15 years. Bob may or may not realize who Alice is.

In short, this is when a familiar voice reveals the identity of a character in a moment that is shocking to the audience and/or other character(s). See also Hey, It's That Voice!, where the audience recognizes the voice actor.

Anime & Manga

 * Late in Monster: Eva Heinemann realizes that . She'd spoken to him over the phone once or twice, but when she heard his voice in person, it hit her like a ton of bricks.

Comic Books

 * In the Tintin book Land of Black Gold, Tintin wonders about the saboteur leader's voice. It turns out to be Dr. J.W. Muller from The Black Island.

Film

 * Death and the Maiden: When Paulina Escobar hears Doctor Miranda speak and laugh, she recognizes his voice as that of the man who was in charge of her torture and rape by government thugs years earlier.
 * Collateral Damage had a bad guy identified that way.
 * Who Framed Roger Rabbit?: "Remember ME EDDIE, When I killed your brother! I TALKED JUST LIKE THIS!!!"
 * Tom realizes that Shaker was his son's kidnapper in Ransom when he sees his son Sean's reaction to his voice.

Literature

 * In Discworld, many people die and don't realize that they're dead until they hear the distinctive voice of fan-favorite, who always
 * Works on the readers, too. Sometimes, Death will just show up and say a line or two without ever being explicitly identified to anyone but the reader via the dialogue.

Live-Action TV

 * "The Man" on Alias
 * On an episode of Burn Notice, Season 2 ("Bad Breaks"), Michael is unexpectedly stuck in a bank in the middle of a robbery. He pretends to be a doctor, which gives him various opportunities to cause trouble for the bad guys. After many fun shenanigans, Sam ends up calling the head bank robber on his cell phone, pretending to be a powerful, scary guy who "really owns the bank". Michael confirms that he "recognizes the voice", and relates a story about what a powerful, scary guy Sam is, which causes dissension in the ranks of the remaining robbers.
 * On Smallville, Clark occasionally phoned Lois as "The Red and Blue Blur" using a voice modulator to disguise his voice. One time (when we discover that Chloe has a tap on his phone, and on all the other phones in the world) some Meddling Kids mess with Chloe's setup, rendering Clark's modulation ineffective, and she heard his real voice.
 * Twice on The Muppet Show a mysterious character appears with a mask - a black knight in one episode, a Darth Vader parody on another. But when the character speaks, it is clear by his distictive voice that it's Gonzo. That and the nose.
 * An episode of Married... with Children has the NO MA'AM men horrified beyond belief when Peggy's horrifically obese mother demonstrates that she is the voice behind "Butter", the phone sex girl they'd been talking to.

Tabletop Games

 * Dungeons & Dragons adventure "Night of the Vampire": When Lady Constantina is impersonated by her maid, the players can recognize this by the difference in their voices on the audio CD track.

Western Animation

 * Totally Spies! episode "Miss Spirit Fingers (Jazz Hands' Return - Part 2)": While Alex and Clover are eavesdropping on a conversation between the villain Jazz Hands and Miss Spirit Fingers, they notice that Miss Fingers has the same voice as Sam. They realize that Sam is masquerading as Miss Spirit Fingers and (wrongly) conclude that Sam has defected and joined Jazz Hands.
 * A Running Gag on Rocky and Bullwinkle is that whenever they meet Boris in disguise, Rocky always asks "That voice! Where have I heard it before?" In one episode, Bullwinkle answers, "In about 365 other episodes, but I don't know who it is either."

Real Life

 * Notorious spy Robert Hanssen was finally caught when the FBI, which had focused in on a different person as the suspect, obtained a voice recording of the spy and the agent who listened to the tape recognized Hanssen's voice.