Who and when introduced a rule that fictitious telephone numbers given in movies are to start with "555"?

In North America, telephone numbers with the prefix 555 are widely used for fictitious phone numbers in television shows, films and other types of fictional media.

Not all numbers that begin with 555 are fictional—for example, +1-[areacode]-555-1212 is one of the standard numbers for directory assistance throughout the United States and Canada. In fact, only 555-0100 through 555-0199 are now specifically reserved for fictional use, with the other numbers having been released for actual assignment. How, exactly, this will interact with the many uses of 555-2368 (long the "standard" fake number) by AT&T and other telephone companies, is no clearer than the reason for the choice of "2368".

The phone companies started encouraging the producers of television shows and movies to use the 555 prefix for fictional telephone numbers, roughly during the 1970s. One of the earliest uses of a 555 number can be seen in A Patch of Blue (1965), with 555-3268. In older television shows from the 1950s or 1960s, "KLondike 5" or "KLamath 5" was used, as at the time the telephone exchanges used letters. The Simpsons used a variation of this in some of their earlier seasons by having the phone number start out with KL5 (for example, Homer Simpson's Mr. Plow business used both KL5-3223 as the home number and KL5-3226 as the business number. Barney Gumble's Plow King phone number was KL5-4796 in the commercial sung by Linda Ronstadt)

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In the US, the prefix 555 is only used for informational type reference calls (i.e. 1-555-1212 for Directory Assistance) or else fictional numbers -- no real subscribers have this number prefix anywhere in the country. It prevents someone from having their number be in a film and then being called up constantly by fans or people who heard the number.

That has happened a lot with music (for example, the song "867-5309 "Jenny" drove those people nuts with calls asking for "Jenny")

Didn't think it was a rule. Think it comes from dialing information for out-of- area code areas. (Like you want L.A. information, you dialed 213-555-1212.) It's easy to remember, too.

555-2368

I don't know when exactly but it was set aside for the film industry to use. There are some real numbers that use these first 3 numbers but most of the time its for the entertainment industry.

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