Voicemail Confusion

When someone calls another person on the phone, usually because of some urgent matter, the caller gets a greeting, usually "hello" or something like that, and the caller tries to speak to them, but realizes that the greeting was actually a voicemail recording.

If the caller talks for a while and the answering machine reveals itself right after he finishes, that means that the person who recorded the message knew exactly how long the caller would talk, making it an example of The Tape Knew You Would Say That as well.

Examples of Voicemail Confusion include:

Film

Sarah Connor's voicemail greeting in The Terminator. Subverted in that no one is fooled by it.
I'm Gonna Git You Sucka. When Kung Fu Joe calls Slade, Slade answers. Kung Fu Joe warns him that the police are after them.

Slade: Fooled you! I'm not home right now. Leave your name and number. I'll call you back. Thanks for calling. Bye.

Live-Action Television

One episode of Cheers involves Sam's message, which sounds like him answering the phone, then a long pause, followed by "Just kidding. You got my machine." Diane calls Sam before her wedding to Frasier, hoping Sam is on a plane on his way to stop the wedding. When she thinks he has answered, she hangs up in disgust without hearing the rest, and thus doesn't know that Sam is on his way.

Music

Inverted in Blake Shelton's song Austin. Earlier in the song, a woman attempted to call an ex-boyfriend for whom she's realized she still has feelings, only getting his answering machine. When he calls her back, she imitates the messages he'd had on his answering machine, ending with:

And by the way, boy, this is no machine you're talkin' to
Can't you tell, this is Austin, and I still love you.

Web Original

From That Guy With The Glasses:

That Chick: Oh, by the way, this has been an answering machine the whole time. Leave your message after the beep! * beep!*

Western Animation

This has become a running gag in Archer, the titular character has many intricate versions of this. At one point, he says the exact time to try and convince his mother it is really him.
Parodied and inverted in an episode of The Simpsons, where Homer initially thinks Stephen Hawking's "voice" is a recorded message.