Hollywood CB

"Uh, 10-4 Pig-Pen, what's yer 20? Omaha?!"

—Convoy, C.W. McCall

Anybody who has used a two-way radio, or even a walkie talkie, knows that there are certain rules. You need to wait until the other person is finished talking (thus the reason for the oft-lampooned "Over"). There are range limits. Two people talking at once sounds like garbage. While there are plenty of frequencies, and you need to coordinate which one you'll be on, other people use them too. Sometimes people aren't sitting right next to the radio, or don't have it turned on, so they won't reply immediately.

In Hollywood Science, when you talk into the radio, the radio has at least as much range as you need, the person you want is on the line—and just them, unless the plot requires someone to eavesdrop. You can interrupt conversations, talk over someone else, and everybody hears you just fine. Sometimes two people can be heard at once. Except for a little well-timed Walkie-Talkie Static, everything is perfectly clear.

Named for the most common culprit, the Citizens' Band (CB) radio.

Examples of Hollywood CB include:

Film

Die Hard averts this. McClane gets a bad guy's walkie-talkie, and talks to Al the policeman, and it's made clear that the bad guys can hear everything he's saying, hence why he goes by "Roy" instead of using his real name.
- Also plays it straight, when McClane is able to interrupt Hans in mid-sentence.
- In Live Free or Die Hard, McClane uses the bad guy's CB's to contact the FBI. Partially justified in that he knew the correct frequency and had a world-class amateur hacker working for him In a World where hacking can do goddamn everything.
Smokey and the Bandit
Everybody in The Cannonball Run seems to have their CB radio tuned to the same frequency. Possibly the racers had agreed to a specific frequency before the race started, but also they have no trouble communicating with plenty of random truck drivers during the race.
- Relatively justified since in the CB heydey channel 19 was a de facto standard for truckers on the interstate; there were exceptions for specific routes but they were pretty well known. Maybe they simply stayed on 19, or changed to 19 when they wanted to talk to a trucker.
In the first Tremors movie, the people of Perfection use a CB radio to warn the Gummers of impending Bad Things possibly coming their way. Actually justified in this case, since it's made clear that they can't reach anyone outside their valley with their CBs, and it would make sense for everyone to use the same frequency.

Live-Action TV

The Dukes of Hazzard—Anybody could pick up his CB and call anyone, and that person was on that frequency.
BJ and the Bear
The Charlie's Angels episode "Angels Go Truckin'".
The walkie talkies on Lost—The signal can travel long distances (even to a nearby island.)
- To be fair, the Island did have plenty of man-made constructions, and it is possible that the Others may have built a repeater to extend the range. (according to Lostpedia)
Memorably subverted in The Young Ones, in which Neil is instructed to make the static noises himself when using his police walkie talkie.

Music

The song "Convoy" and the film it spawned.

Video Games

Your radio in BioShock (series) is automatically tuned to Atlas' radio frequency the second you pick it up, and other people (Like Sander Cohen or Andrew Ryan) can easily tune in, jam your connection and talk to you.
Dialed Up to Eleven in Metal Gear Solid - The "Codec" supposedly puts the sound straight into your earbones so only you hear the person talking to you (with ample opportunity for Fridge Logic, considering the speaker's own voice should still be very audible to their surroundings - this becomes particularly ridiculous in Metal Gear Solid 2: Sons of Liberty, where characters standing barely two feet away from one another will decide to switch to nanocommunications for privacy). Plus, despite supposedly being an audio-only device, the HUD displays it almost like a videophone. On top of that, you have a number of people whose frequencies you have to find.
- The "speaker's own voice" issue could probably be Handwaved by invoking subvocalization—methods of turning it into audible speech have appeared in science fiction at least as far back as Neuromancer.
- Metal Gear Solid 3: Snake Eater's radio was essentially the same as the above Codec, though it also worked around the "speaker's own voice" issue by having Snake communicating back to Mission Control via a throat mike.

"This here's the Rubber Duck on the side--We gone, Bye, Bye..."