Good news, tragically single geeksters: The next time you manage to get a phone number from a romantic prospect that begins with the dialing prefix 555, it’s possible that the target of your affections isn’t giving you a pop-culture-inspired brush-off. Possible, but not likely. That’s because, contrary to what conventional wisdom and years of movie- and television-consumption may have taught you, not every U.S. telephone number beginning with 555 is fake. Just lots of them.

The North American Numbering Plan — which has been the governing document for assigning and maintaining telephone numbers in the United States, Canada, Mexico, and various nearby countries since 1947 — was amended in 1994 to formally reserve exactly 100 telephone numbers for fictional use. That is to say, any telephone number falling between 555-0100 and 555-0199 would never be placed in service, and instead be reserved for use in movies, television, and other mass media works of fiction. Thus, if someone you chat up hands you a 555 phone number outside that range, they may not be scamming you. That said, most active 555 numbers are used by businesses or service lines, so odds are you are still being duped, but it’s not a dead certainty.

The need for “fiction-safe” phone numbers is fairly straightforward; if a phone number becomes an element of pop culture, a certain percentage of fans will be unable to resist dialing it to see who answers, creating a nuisance for whichever poor sap happens to share a number with a fictional character or organization. Tommy Tutone’s famous “867-5309/Jenny” pop song has been the classic example of this phenomenon.

In fact, fiction-safe phone numbers predate the 555 rule. Until the early 1970s, AT&T kept a list of inactive but potentially “real” phone numbers that it shared with Hollywood, but by 1973, every possible seven-digit phone number was in use somewhere in the United States. Thus, from 1973 on, the 555 exchange became Ma Bell’s recommended fake phone prefix. In 1994, further demand for additional phone numbers forced the reserved list down to just 100 phone numbers under the 555 exchange.

Still, one quasi-fictional 555 telephone number from outside the 0100 to 0199 range remains a prominent fixture in Hollywood productions, as it has some traditional significance that predates the existence of not only fake 555 numbers, but 10-digit phone numbers altogether.


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The quasi-fake telephone number that Hollywood just can’t give up is 555-2368, which is decidedly outside the 555-0100 to 555-0199 range of reserved fictional dialing codes.

Many of you may recognize this as the “Who ya gonna call?” hotline used to reach The Ghostbusters. It’s also the professional phone number to reach private detective Jim Rockford, the home phone of bionic woman Jaime Sommers, the Guilers’ home phone from Close Encounters of the Third Kind, the number of a motel room in Memento, and the desk phone of police detectives Tony Baretta, Rick Hunter, and Theo Kojak, all of whom had shows titled after their last names. This list is far from exhaustive but should serve to illustrate just how popular this fictional phone number was and continues to be, especially considering that it stopped being certifiably fake after 1994.

So what, exactly, makes this particular fake number so popular with Hollywood writers and producers? Tradition.

Before 10-digit dialing codes, the U.S. phone numbers employed letter-number combinations formatted as two letters, followed by as many as four numbers. The two-letter prefixes were extended into memorable colloquial names, such as Butterfield for BU (as in the film, Butterfield-8). During this period, the KL exchange was reserved for fictional use, resulting in famous fake telephone numbers like Klondike 5-4385, the number for Doc Emmett Brown’s 1955 home in Back to the Future. That said, the KL exchange was not the preferred choice for many writers of fiction (and fictional phone numbers).

AT&T maintained a Central Exchange in every major metropolitan area for most of the mid 20th century and advertised the contact number of these exchanges rather heavily: Exchange-2368. The 2368 was the numeric conversion of CENT, for central, using the letters assigned to digits on a telephone dial. Thus, when writers would “invent” phone numbers, they would often end them with 2368 so they would sound familiar and plausible, thanks to the phone company’s promotion of Exchange-2368.

When the 10-digit, 555 fictional phone number era came into use in the late 1960s and early 1970s, writers simply converted Exchange-2368 to 555-2368, preserving the traditionally fake phone number. That tradition continues today, even though real people could conceivably apply for the 555-2368 number in various U.S. area codes.

That’s not just some interacting integration of insularly important integers; it’s a numerically notorious notion of noteworthy Geek Trivia.

The quibble of the week

If you uncover a questionable fact or debatable aspect of this week’s Geek Trivia, just post it in the discussion area of the article. Every week, yours truly will choose the best quibble from our assembled masses and discuss it in a future edition of Geek Trivia.

This week’s quibble comes from the Sept. 16, 2008 edition of Geek Trivia, “The fact of the (anti)matter.” TechRepublic member Dr_Zinj dinged me for misrepresenting the current state of antimatter containment technology.
Check out this week’s quibble.

The quibble of the week

“Jay, you said, ‘Part of that has to do with human beings having no way of storing antimatter, though presumably one could create ionized anti-helium atoms and store them in a magnetic bottle.’ Actually, we do have, and have had, a way to store antimatter. A ‘magnetic storage bottle-type’ device, also called a ‘high vacuum magnetron trap’, and typically referred to as a ‘Penning Trap,’ has been around since the year I was born, 1959. More to the point, those same guys at CERN have been using a ‘Penning-Malmberg’ trap since roughly late 2002 to actually store tens of thousands of antimatter atoms. Unfortunately, even at peak production, CERN would require, ‘two billion years to produce 1 gram of antihydrogen'[link]. The biggest problem with using magnetic storage containers is that the particles stored inside need to have a charge or they can’t be confined.”

Yeah, this was one of my grosser misstatements, as I was trying to convey the notion that most individual antimatter particles can’t be practically stored; it requires the creation of full antimatter atoms, which can then be given a magnetic charge, and thus stored in a magnetic bottle, as is done with a Penning Trap. Storing, say, an anti-neutron all by itself is beyond our technology right now, so far as I understand it, but I did not communicate that clearly.

Thanks for the particle physics comeuppance, and keep those quibbles coming!

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