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Useful Notes / North American Numbering Plan

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A bit about making phone calls in the United States, Canada, and select other areas.


Two reasons. First, it allows you to make a realistic-looking phone number in the countries it covers (including the United States, the biggest media producer and fairly likely to be your home country), while avoiding the obvious fakeness of the 555 number. And second, it allows Tropers who are very knowledgeable about these things to talk at length about them (with the excuse of the first reason, of course). Every time you think this site can't get any nerdier, we do our best to prove you wrong, dear reader!


The fact that it's called the "North American Numbering Plan" should clue you in that it's not just a U.S. thing, or even a U.S.-Canadian thing. The NANP covers 25 distinct regions in 20 different countries throughout the North American continent and the Caribbean. It doesn't cover all of North America — Mexico is the biggest holdout — but it covers a surprising amount of it. It also covers some areas that aren't technically in North America at all, mostly U.S. territories in the Pacific.

The full list:

A brief history

From the invention of the telephone in 1876 through the first part of the 20th century, the telephone system in the U.S. and Canada was operated by regional and local telephone systems which formed part of the Bell System. Each system had a numbering plan which divided the area into "central offices" or "exchanges", which in turn assigned numbers to individual subscribers in the areas they handled.

The defining feature of the exchanges is that they were identified by two letters, typically the first two letters of the area the exchange served or some other memorable name, which was dialed as a very short Phone Word. Works from this era demonstrate this convention; for instance, the Hotel Pennsylvania in Manhattan, a major venue for Big Band music, inspired the song "Pennsylvania 6-5000", famously performed and recorded by Glenn Miller and his band.note  If you wanted to dial that number, you would use the first two letters of "Pennsylvania" to get "PE 6-5000" — turning that into all numbers (which wouldn't be standard until 1958) would get you 736-5000, which was indeed the local number of the hotel's front desk and remained so until the hotel's closure in 2020. One interesting exchange you may have heard of is "Klondike", as many works of the time had numbers going "Klondike 5-xxxx". "KL" spelled "55", and that's how you get a 555 number.

The system was far from uniform. Most central offices used two letters and five numbers, but a fair number used three letters and four numbers, smaller exchanges used two letters and four or even three numbers, and a few even used both four and five numbers. Needless to say, this mishmash of incompatible local systems proved to be a major obstacle for long-distance communication.

In 1947, the Bell System, in cooperation with independent local phone companies, established a new numbering plan across the U.S. and Canada. The two countries were divided into 86 "numbering plan areas" that were all assigned a three-digit code, formally called an "NPA code" but commonly known as an area code. Back in the day, people weren't expected to know these codes; instead, they called an operator and asked them to hook them up to a particular city, and they'd be expected to know the area code based on what you told them. But over the years, the system standardized so that every local number was seven digits, allowing people to dial directly to any other number in the NANP with just ten digits — the three-digit area code and the seven-digit local number.

How it was designed

The way it worked was pretty clever. Phones were pretty primitive at the time; they needed to know not just what number you were dialing, but when to stop. Since you couldn't use 0 or 1 to spell out a Phone Word, the Bell System realized that the former central office number cannot contain a 0 or 1. They took advantage of this when building the system:

  • If the phone detected that neither of the first two numbers were 0 or 1, it would know the number was a seven-digit local number and start the call after you dialed seven digits.
  • If the phone detected that the first number was a 0, it would give you the operator.
  • If the phone detected that the first number was a 1, it would ignore it, because the way phones worked back then a "1" could easily be dialed accidentally just by pulling the receiver off the hook.
  • If the phone detected that the second number (but not the first or third) was a 0 or 1, it would know the number was a ten-digit long-distance number and start the call after you dialed ten digits.
  • If the phone detected that the second and third number were both 1, it would dial a special three-digit number.
Because of this, area codes were designed with the middle number being a 0 or 1, with the first number being between 2 and 9. This allowed for more than 100 possible area codes; 86 were originally assigned, with lots of space for expansion. Within that scheme, there was a strict division of which area codes had a 0 or 1 in the middle. Area codes that encompassed an entire state, province, or territory had a 0; area codes that only covered part of a state or territory got a 1. The lower the first and third digit, the more "important" the area was considered. The area code 212, which had to go to a region that covered only part of a state, went to New York City; 213 went to Southern California. The area code 201, which had to go to an entire state, went to New Jersey; 202 went to Washington, D.C. There was a practical element to it; the smaller numbers were faster to dial on a rotary phone. The "x11" combination of area codes was reserved for other use.

Expansion beyond the U.S. and Canada

The 1947 plan originally included just the U.S. and Canada. But in 1958, Bermuda and the British West Indies were added to the plan, at the request of the British government, who noted that their telecom systems had historically been administered through Canada. After this, the rest of the Caribbean debated whether they wanted to join. Some did, like the Dominican Republic and several U.S. territories like the U.S. Virgin Islands. But others did not, like Cuba, Haiti, and the French and Dutch Caribbean; the one exception is Sint Maarten, the Dutch part of the island of Saint Martin, which didn't join until 2011.note  Mexico and Central America decided not to join either, even though the NANP had already assigned three area codes to Mexico.

While Hawaii was part of the NANP from the start, U.S. possessions in the Pacific were not, getting their own international calling codes. That changed around the Turn of the Millennium, when they joined the NANP and had their former country codes turned into their NANP area codes.

Changes over time

The system evolved over the years into what we see today:

  • The Phone Word was a fact of life for years after the NANP was introduced. "All-number calling" wasn't introduced until 1958, and even then it was simply because many parts of the country had run out of number combinations that could be expressed by a memorable name.
  • In spite of the system being set up for it, ten-digit dialing also wasn't an option from the start; you generally still had to call an operator to place a long distance call. "Direct distance dialing", which would allow a customer to bypass the operator with the ten-digit number, didn't launch until 1951 — and even then, only 12 cities, all in the U.S., had the switching equipment to allow it. It wasn't until The '70s that the whole country had ten-digit dialing, and popular culture would reference the "operator" well into that decade (e.g. the 1972 Jim Croce song "Operator (That's Not the Way It Feels)", in which the singer unloads on the operator while trying to reach his ex-girlfriend).
  • Although the system had included North American countries other than the U.S. and Canada since 1958, it wasn't until the 1970s that it formally adopted the name "North American Numbering Plan".
  • The Bell System administered the NANP until The '80s, when it was broken up in a major anti-trust action. The Federal Communications Commission took over, assigning the day-to-day operation to the "NANP Administrator". In more recent decades, the NANP Administrator has been a private contractor. Each participating country has full control of its numbering resources, but all cooperate with NANPA.
  • The "x11" series of area codes became special numbers with just three digits. The most famous is the emergency number 911, which wasn't a widespread thing until the 1980s; before then, you basically had to dial the operator and ask them to call the emergency service you wanted, because they had the phone number handy. Most of the other combinations are assigned to more mundane things, which may vary from place to place but are usually the same (e.g. 311 for municipal government and non-emergency services, 511 for traffic information, 811 for locations of public utilities and disseminated through "call before you dig" campaignsnote ). The emergency number 911 is easily the most famous, known around the world through Eagleland Osmosis — so much so that many countries around the world will reconnect "911" to the proper emergency number there if it's different.
  • The "Offer Void in Nebraska" trope originated in Bell System rules. The trope's analysis page provides more details, but the most relevant one for the purposes of this page is that for decades, a single toll-free number could not be used for calls within a state and calls between states. Since almost all toll-free call centers in the Bell System era were in Nebraska (again, see the analysis page for why), essentially all national advertising offers that included a toll-free number included the phrase "offer void in Nebraska". This restriction on usage of toll-free numbers, which was inherent in the original structure of toll-free calling, survived the breakup of Ma Bell. It wasn't until the 1993 introduction of toll-free number portability, which allows the owner of such a number to use it with any long-distance carrier, that a single toll-free number could be used for the entire U.S.

Eventually, more area codes were introduced as the existing ones ran out of numbers. Originally, area codes were expanded by splitting them geographically; everyone kept their local number, but one region would get a new area code, and expansion would happen from there. In more recent decades, starting in 1992, area codes were added as an "overlay" — the new code would have the same geographic area as the old one and not pick up any existing numbers. However, area code splits still took place for more than a decade afterwards; the last area code split to date was in 2007 in New Mexico.Aside 

By this time, the plan ran out of the area code combinations with 0 and 1 in the middle number. But phone technology had moved from rotary phones to "touch-tone" dialing, the more familiar style with the buttons, so it was much easier for a phone to tell when you've stopped dialing and given the full number. This allowed for area codes with a number other than 0 or 1 in the middle, first introduced in 1995.

Interestingly, one restriction to the new area codes is that the NANP will not assign a code with the same three digits in a row, the idea being that one particular area shouldn't have an area code that's that much easier to remember than another. Nevada found this out the hard way when it was split into two area codes in 1998. With Las Vegas' home of Clark County set to retain 702 (seeing that it had about three-fourths of the state's population), it requested that the rest of the state get area code 777 (a reference to a "lucky" slot machine combination). This request was turned down and they got stuck with 775.

Modern quirks

The modern system has many peculiarities given the way it has evolved, now that the phone doesn't have to guess how many numbers you're trying to dial:

  • Without the technical limitations of the rotary phone, a number can now start with 1. The prefix 1 was originally used for toll calls, but came to be required for all long-distance calls from certain exchanges, turning a ten-digit number to an eleven-digit number.
  • You can dial more numbers past 0 without dialing the operator. This is usually used for dialing an international number (well, outside the NANP), which uses 011 followed by the country code and the number.
  • The prevalence of overlay plans confused phones so much (for lack of a better term) that many area codes did away with seven-digit local dialing; now you had to dial ten or eleven numbers for every number, local or long-distance. In some places, you had to use ten-digit dialing for the overlay code and eleven-digit dialing for long-distance calls. Given the prevalence of cell phones that won't even start the call until you press the right button, in most cases the phone will understand what you're trying to do and dial the right number anyway. Speaking of cell phones:
  • The NANP is unusual in the world in that for the most part, it does not assign special area codes to mobile phones.note  Instead, they get geographic numbers based on where you live (or, as xkcd pointed out, where you used to live). The advantage is that you can swap a local number between a landline and a cell phone in either direction; it also allows you to keep your number when you change carriers, which is often not possible in other countries that assign specific blocks to certain mobile carriers. The disadvantage is that incoming calls need to be routed through equipment in that geographic area, meaning that if service is knocked out there, your cell phone might not receive calls (although it can send them)note . It also meant in the early days that it wasn't possible to charge more for calls to mobile phones than to landlines, meaning that more often than not it was the cell phone user who paid extra (which was perceived as fairer — you pay for the convenience of using a cell phone).note 
  • The area code 800 was historically assigned for toll-free dialing, and over the years, many a Phone Number Jingle has started with "1-800" — especially if the rest of the number was a Phone Word. With the expansion of area codes, the "8xx" range of codes has been assigned to toll-free numbers like 888, 877, and 866. There also exists area code 900, a pay calling line (what the UK would call "premium rate") usually used for competitions and phone sex lines; it has a local number equivalent, the 976 exchange, as seen in the 1988 horror film 976-EVIL (and its 1991 sequel).
  • It's possible now to do special three-digit numbers outside the "x11" paradigm. It's not very widespread; the most visible is 988, implemented in the U.S. and Canada as a suicide prevention hotline.

Over the decades, the NANP has ingrained itself into the psyche of the North American public. Phone numbers have long been written in the "xxx-xxxx" format, and it's become something of a mnemonic to allow people to easily recite a long number. In more recent decades, certain cities have even begun to identify with their area code; the Trope Maker is generally believed to be the city of Toronto, which in slang is known as "the 416". With the expansion of area codes to include suburbs and overlay plans, it also denotes someone who's really from Toronto proper, who'd be able to prove it with a 416 number. (The Toronto suburbs hit back by calling the area "the 905".)

The 555 trope survived from the pre-NANP days; while officially, only 555-0100 to 555-0199 are set aside for fictional examples, in practice pretty much all 555 numbers are fictional. It's pretty much necessary, because if you give a valid number in a creative work, people are going to try calling it (see, for instance, what happened with Jenny's Number). But seven-digit local numbers still can't start with 1 or 0, like in the old days, so the easiest way to subtly get an invalid number on screen is to use a number like that.

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