In our modern day and age, when communication needs to take place, we can do it with landlines, Cell Phones, text messages, and/or The Internet.
It is a really good thing, too, because when the hero(es) need help, this trope comes into play.
There's a situation that's too big for our main character to handle on his/her own. But he/she knows a good number of people, perhaps because they are popular and friendly, or just from Walking the Earth. Either way, it's time to enlist their aid, and because the heroes are the heroes, anyone called on the phone is only too happy to pitch in and help. Not only that, but they're willing to call the next person in the chain of phone numbers to help get the giant group effort underway that much sooner.
A variation common in older productions: the viewer is treated to a splitscreen as more and more people become involved in sending the message out.
Can be subverted, particularly online or in print, by Astro Turfing.
- In Young Avengers #11, Prodigy texts a couple of friends to run interference for the team while they get close to the Big Bad. They texted some friends and... The next pages shows a telecom tree of young heroes that has expanded to fill a full page.
- Global Frequency has this as its premise, with 1,001 people with specialized abilities or skills spread across the world ready to be summoned by a phone call from either Big Good Miranda Zero or Mission Control Aleph. Though only a couple of agents are actively involved in any particular crisis, there are a few times when the call goes out to all 1,001 members for any help they can provide (notably the the last issue of the series).
- In Practical Magic, when witches Gillian and Sally need extra help to get rid of the nasty ex-boyfriend ghost of Jimmy Angelov they activate the town Phone Tree, normally used to let all the moms know of school snow days. It turns out that despite the Gossipy Hens talking smack about the witch sisters, most of the women in town are not only genuinely curious about them, but happy to pitch in because they can identify strongly with having a bad ex who won't go away without a female friend having her back.
- In Spy Kid 3 D Game Over, the Cortez children send out a desperate wrist phone call to "Everybody!". Their parents and grandparents show up, as well as their uncle Machete, Floop and the reformed Minion, the reformed Uncle and Giggles families, the Mad Scientist, the guy who owned the theme park at the start of the second movie and his son.
- Brandon and his friends do this for Jason Nesmith in Galaxy Quest.
- In Legally Blonde 2, one scene involved the sorority the lead is now in activating an emergency phone tree of ex-sorority members.
- Buckaroo Banzai has the Blue Blaze irregulars, a group of various people who help him out of tight spots. No matter what it is or who they are.
- In a movie about retired Mafia members living in Florida, one of the group uses the fact that he has kept in touch with every other former Mafioso to have retired to the greater Miami area to gather a posse to raid the base of a crime lord who had kidnapped the daughter of another member of the group. This leads to a hilarious scene where a freighter owned by a drug lord is attacked by a busload of gun-toting senior citizens.
- Working to a deadline? Need a mob to storm the castle? Just tell a member of the Ogg family. The rest will take care of itself.
- Known as the ghost-to-ghost hookup in The Three Investigators books.
- In The Executioner novel Dixie Convoy, the truckers helping Mack Bolan use CB radio to spread a message from one coast of the US to the others.
- Doctor Who series 6 (or 32) does this twice. Firstly, A Good Man Goes To War is all about this, with the Doctor calling in several favours to raise an army to rescue Amy and her baby. Secondly, in The Wedding of River Song, River, Amy and Rory construct a device to send a distress signal outside the collapsing Alternate Universe they're trapped in, asking the whole universe for help, as the Doctor is about to die. Literally billions of races across the universe agree to help. While this doesn't actively do anything, it breaks the Doctor out of his Heroic BSoD and reminds him that however much death and destruction he leaves in his wake, he's still a hero, and his life is worth something.
- In The Nanny, when Fran gets engaged, she calls her mom, who puts her on hold to talk to someone else. She tells them. They call someone else, and so on, and so on, and so on. Each time, a picture of that person is added to the screen. By the time mom gets back on line to Fran, everyone knows.
- In the music video for Tracy Lawrence's "Find Out Who Your Friends Are", a redneck's truck breaks down in the middle of nowhere. He places one cell call to a friend before his phone fails, he then gives up. Fortunately for him, his friend has friends, and those friends have friends... until a giant convoy of friends is seen converging on him, in everything from a tractor to a Jeep to a Corvette.
- In Bye Bye Birdie the teenagers of Sweet Apple Ohio are seen doing a tree in "The Telephone Hour."
- In this case there's no particular help needed, they're just spreading the news that Hugo and Kim are now an item, and there's one poor sap (Harvey Johnson) who's trying to get a date.
- Telefang: Ubiquitous thanks to the summon-monsters-by-phoning-them mechanic.
- Shows up in El Goonish Shive after Hedge kidnaps Elliot.
- There she is!!, in its final episode, has Nabi the cat trying desperately to get to the airport before his girlfriend Doki leaves. All the friends and relatives who have been with them since episode 2 pitch in and help get him there, including calling forward to help stop Doki so Nabi has his chance to get there.
- In Beverly Hills Teens if you wanted to get everybody together you told Switchboard, and pretended it was a secret.
- The finale of Justice League Unlimited doesn't go tree style, but they do summon every single member for the final fight, even allowing the bad guys to fight to save the world.
- Whenever she has to travel to some remote location, Kim Possible can always count on someone she has helped before to provide free transportation.
- There is an episode or a longer special of The Fairly OddParents where Timmy sends a message over the internet requesting help from all the kids in the world.
- Marge Simpson has a diagram of her phone tree.
- In Tex Avery's Tortoise Beats Hare, Bugs Bunny has challenged Cecil Turtle to a footrace. Cecil calls his old buddy Chester and together they set up a Ringer Ploy over a phone tree.
- On school field trips, there's a very large web of people that would be contacted in case of an emergency. If something happens to a student, cue the telecom.
- Flash Mobs are created through ever-widening circles of text messaging.
- A man was arrested in a foreign country. He posted one message to Twitter, and the resulting response web alerted his bosses and got the problem resolved with the foreign authorities.
- Several companies with multiple retail locations have a phone tree set up with each store in a given area responsible for calling one other pre-designated store, so that (for instance) if an unsuccessful shoplifter successfully flees note , other locations can be quickly forewarned.