Tin Can Telephone

"It's The Homestar Runner, speaking into an empty soup can, with a length of twine coming from the 'neath. Hello, empty soup can. Hello, length of twine."

—The Homestar Runner, Marzipan's Answering Machine Version 13.2

Ah, childhood. Treehouses and sleepovers and talking to your friends on tin can telephones. It's made of junk: just two old tin cans and a length of string, but it's the stuff that memories are made of. Occasionally you can see a variant that has a tube that travels underground. This variant is derived from early nautical vessels.

Truth in Television, of course, although the real thing only works if there is no slack in the string at all. In visual media, the string is just as likely to be portrayed as slack or winding its way around, under, or over things, which wouldn't work.

Of course, now that cellular phones are cheap enough that even children have them, this is a sadly disappearing relic.

Examples of tin can telephones include:

Advertising

The Mueller commercials used this.^[context?]
Also used by Progresso here, among other examples.

Anime and Manga

A chapter of Yotsuba&! has Yotsuba, Miura, and Ena playing with paper-cup versions. Yotsuba keeps hers, which shows up in later chapters as her "cell phone".
An episode of Hanamaru Kindergarten has two toddlers playing with one of these only a few feet long, in a very loud classroom.
Negima Second Season: Kaede and Setsuna tried to make these work between their rooms however as Konoka explained they don't work between doors, much to their dismay causing them to gain +5 Absentmindedness and -3 intelligence, however it lets them hear the invisible Cute Ghost Girl nearby leading to screams.
Tamako Market: Tamako and Mochizo use one to talk when they're in their bedrooms - which are across a narrow street from each other. In one episode, they get a bad line... when a bird perches on the string.

Comic Books

One of the official Sly Cooper tie-in comics shows the gang pulling their first heist as gap-toothed youngsters in the orphanage, the cookie jar caper, using one of these as a communicator. When Sly is almost sprung, it, seemingly accidentally, doubles as an extraction device, with Sly being pulled to safety before he is spotted when Murray pedals the getaway trike away.
They've probably done this in The Beano or The Dandy at least a hundred times.
One Donald Duck comic had Huey, Dewey, and Louie set one up between Donald and Neighbor Jones after their feuding starts taking its toll on their house. "Have a war of words!" Unfortunately, Jones feeds the business end of a live-wire to his can, giving Donald a nasty shock.

Film

Exactly what the boys use to communicate with the girl across the street in Three Ninjas.
Scary Movie 2 parodied this. After getting high-tech goggles and weapons, the heroes didn't have enough money for cell phones. So they used tin cans. Tin cans that have only about 3 feet of string between them.
Used by the kids in Milk Money.
Short appearance in Walk the Line.
Shaggy and Scooby Doo do this in Monsters Unleashed, except Scooby gets confused and holds the can to his mouth when he should be listening and to his ear when he should be talking.
Used by Adam Sandler and the kids in Grown Ups.

Literature

One of Anthony Buckeridge's Jennings novels features a brief craze for tin can phones at the title character's school.
In Henry and the Paper Route (in the same world as the Ramona Quimby books), Henry Huggins is excited when a boy his own age moves into the neighborhood. In his first conversation with the kid, Henry suggests a tin can phone, but he's told that it probably wouldn't work and, at any rate, they both have actual phones in their houses.
Kristy of The Baby Sitters Club recollects doing this with Mary Anne when they were children.
Also appears in Alfons Zitterbacke, a children's book from East Germany. It doesn't work, probably because they knot the string to places (they're trying to make a really long line, between their respective rooms).
In Nancy Springer's They're All Named Wildfire, the two main characters live in the opposite sides of a duplex. They drill a hole in the wall so that they can pass a string through to use a tin can telephone. (Interestingly, the fact that the string has to be taut rather than slack is mentioned, as it affects the position of the hole they create.) The tin can telephone becomes thematically important as a symbol of the Power of Friendship in opposition to racism.

Live-Action TV

Mister Rogers' Neighborhood: The Neighborhood of Make Believe has tin phone cages that lower out of nowhere, allowing for communication.
Used in Pee-wee's Playhouse with the Picturephone, except this one is actually a telephone. In Pee-Wee's world, *everyone* uses a tin can on their Picturephones.
Dad's Army attempted to use this as a form of emergency communication in one episode but were foiled by the verger with his hedge shears.
Friends:

Ross: It would be so cool to live across [the street] from you guys!
Joey: Yeah--hey, then we could do that telephone thing! Y'know, where you have a can, and we have a can, and, and it's connected by a string!
Chandler: Or, we could do the actual telephone thing.

Mentioned in the second series of Torchwood. Apparently they don't work when the "entire. telephone. network. is down."
Young Blades: In "To Heir is Human," Siroc invents a tin can telephone-like device using metal cups and some string, which he uses to eavesdrop on the Cardinal's Guards.

Newspaper Comics

Used in Calvin and Hobbes once or twice.
Peanuts had them at least twice. In a 1980s Sunday Strip, Lucy gave Charlie Brown part of a tin can telephone for use during a baseball game. In a 1999 strip, Sally was playing with one when she asked, "How do you get an outside line?"
A cartoon in Future Life magazine showed a flying saucer hovering next to an observatory. The alien pilot is talking to the astronomer on a tin can telephone, explaining (paraphrased): "Yes, our technology is ahead of yours in many ways but behind you in others."

Web Original

The Homestar Runner (you know, the 1930s version) was implied to be talking to modern-day Marzipan's answering machine on one of these.
The two hosts of the weekly Wrestlecrap Radio podcast, R. D. Reynolds and Blade Braxton, are implied to be conversing on one of these.
One episode of Happy Tree Friends had Cuddles and Lumpy playing with one. This being Happy Tree Friends, it results in Cuddles' eardrums being blown out.
The GaMERCaT presents: a better voice chat than what Nintendo currently have.

Western Animation

The Wonder Pets receive their calls of distress primarily through a tin can phone.
In The Simpsons, Bart's tin can phone was once wiretapped.
D.W. once bugged Arthur's room with one of these.
- Also, Arthur and Buster sometimes communicated this way.
Used on the Super Mario World cartoon, with coconut halves and vines.
Used a few times on Ed, Edd 'n' Eddy, with some very bizarre Split-Screen Phone Call effects going on (people actually travelling through the string, for instance, or Ed using a sponge instead of a tin can).
Played with in South Park's "Wacky Molestation Adventure": After the kids have taken over the town and the actual phone system is ruined, we see a scene where Cartman yells into a tin can that isn't connected to anything. Then another kid puts a lid on the can and leaves with it. He ends up coming back, Cartman removes the lid and gets a response.
This was done a few times in Hanna-Barbera's version of The Little Rascals.
The farm on the U.S. Acres portion of Garfield and Friends has an entire system of tin cans for when intrabarnyard communication is desired.
In an episode of SpongeBob SquarePants, Squidward used one of these to try and apologize to Spongebob without actually doing so to his face, however the attempt was foiled because Patrick was using the string as dental floss... ew.
In My Little Pony: Friendship Is Magic episode "Party of One" Pinkie Pie uses this to eavesdrop on Twilight Sparkle.
In the Schoolhouse Rock short "Where The Money Goes" the father facetiously suggests to his son that if they stop paying the phone bill they can always resort to using "tin cans and a string."
The Powerpuff Girls: In "Impeach Fuzz", when notorious hillbilly Fuzzy Lumpkins is elected mayor, he replaces the Powerpuff Hotline with a tin can.
This has been used a few times in Recess