About Opentopia
Opentopia Directory Encyclopedia Tools

North American Numbering Plan

Encyclopedia : N : NO : NOR : North American Numbering Plan

 

The North American Numbering Plan (NANP) is a system for three-digit area codes and seven-digit telephone numbers that direct telephone calls to particular regions on a public switched telephone network (PSTN), where they are further routed by the local network. It is applied to the United States and its territories; Canada; Bermuda; and many Caribbean nations.

Developed in 1947 and first implemented in 1951 by AT&T, the NANP set out to simplify and facilitate direct dialing of long distance calls. It initially applied only to the U.S. and Canada, but at the request of the British Colonial Office, Bermuda and the British West Indies (including Trinidad and Tobago, just off the coast of Venezuela) were added to the North American system given their historic telecommunications administration through Canada as parts of the British Empire and their continued close associations with that country.

Despite the "North American" name of the calling plan, Mexico and the Central American countries are not part of the system, although Mexican participation was planned and partly implemented, with direct dialing from the NANP to some parts of Mexico until 1991.

The NANP is administered by the North American Numbering Plan Administration (NANPA).

Current NANP number format can be summed up via the following:

where

For example:

Contents

Dialing plans

Dialing plans vary from place to place depending on whether an area has overlays (multiple area codes serving the same area) and whether the jurisdiction requires toll alerting (a leading 1 for toll calls). The [NANPA's web site] includes dialing plan information in its [information on individual area codes].

In areas without overlays and without toll alerting, calls within an area code are dialed as seven digits (7D) and calls outside the area code as 1 followed by 10 digits (1+10D). Most areas allow permissive dialing of 1+10D even for calls that could be dialed as 7D. The number of digits dialed is unrelated to whether a call is local or toll.

In areas with overlays, local calls are all dialed as 10D. (In New York City, the preferred form is 1+10D but 10D also works.) In areas without toll alerting, all calls to numbers within the caller's area code and overlay codes serving the same area can be dialed as either 10D or 1+10D, while calls to other area codes must be 1+10D. In areas with toll alerting, all toll calls must be dialed as 1+10D. Most areas permit local calls to be dialed as 1+10D except for Texas which requires that callers know which numbers are local and which are toll, dialing 10D for all local calls and 1+10D for all toll calls.

The current profusion of dialing plans is quite confusing, and it appears likely that all areas will converge on 1+10D even in places where other forms are permitted. Residents of areas with toll alerting tend to feel quite vehemently that it is a necessary service, while residents of areas without toll alerting do not necessarily miss it, even though it means they might be charged for a telephone call with no warning.

Charges

Despite the similar dialing format, calls between different countries and territories that use the NANP are not charged as domestic. Calls between the US and Canada are treated as international, although typically charged at lower rates than calls to other countries. Calls to other destinations in the NANP area can be high; for example, it generally costs more to call Bermuda from the US than it does to call the UK or Japan, even though the dialing format is the same. Similarly, calls from Bermuda to US numbers, (including toll-free 1-800), incur high international rates. This was because many of the island nations at the time implemented a plan of subsidizing the cost of local phone services, from directly charging heavier pricing levies on the international Long Distance services. On account of these higher fees, a handful of scams had taken advantage of customers' unfamiliarity with pricing structure to call the legacy regional 809 area code. Some scams lured customers from the U.S. and Canada into placing expensive calls to the Caribbean, by representing the area code (809) as a regular domestic, low-cost, or toll-free call. These scams are currently on the decline with many of the Cable and Wireless service monopolies being opened up to competition thus bringing rates down.

History

In order to facilitate direct dialing calls, the NANP was created and instituted by AT&T, then the U.S. telephone monopoly, in 1947. However, the first customer-dialed calls using area codes did not occur until late 1951. Originally there were 86 codes, with the biggest population areas getting the numbers that took the shortest time to dial on rotary phones. That is why New York City was given 212, Los Angeles given 213, and Chicago 312, while Vermont received 802 (a total of 20 clicks, 8+10+2). Four areas received the then-maximum number of 21 clicks: South Dakota (605), North Carolina (704), South Carolina (803), and Nova Scotia/Prince Edward Island in the Canadian Maritimes (902). Additionally, in the original plan a middle digit of zero generally indicated the number was for an entire state or province, while a middle digit of one indicated that it was for a smaller region.

At first, area codes were in the form N-Y-X, where N is any number 2~9, Y is 0 or 1, and X is any number 1~9. The restriction on N saves 0 for calling the operator, and 1 for signaling a long-distance call. The restriction on the second digit, limiting it to 0 or 1, was designed to help telephone equipment recognize the difference between a three-digit area code and a three-digit prefix to the telephone number. For example, when a caller dialed "1-202-555-1212", the switching equipment would recognize that "202" was an area code because of the middle 0, and route the call appropriately. If a caller were to dial 1-345-6789, the 4 would be recognized as a long-distance call within the area code and routed as such, without waiting to see or guessing at how many digits the caller meant to enter.

In the late 1980s and early 1990s, NANPA (then still part of Bellcore) began to urge and later require all long-distance calls within each area to include the code, so that badly-needed prefixes with 0 or 1 in the middle could be assigned to local telephone exchanges.

Calls to Mexico (until 1991)

Until 1991, calls to some areas of Mexico from the United States and Canada were made using the North American Numbering Plan area codes. For example, to call a number in northwest Mexico and Mexico City before 1991:

From that year, this was discontinued in favor of the international format:

Expansion of area codes

Due to a combination of increasing demand for telephone services (particularly due to widescale adoption of fax and cell phone communications), and the practice of allocating phone numbers in large blocks to companies for issuing, many area codes began to exhaust their supply of available numbers (code "in jeopardy" in telecom jargon), and additional area codes were needed. In general, area codes were added either as "splits" (in which an area code was divided into two or more regions, one retaining the older area code and the other areas receiving a new code), or "overlays", in which multiple area codes were assigned to the same geographical area. Subtle variations of these techniques have been used as well, such as "dedicated overlays" (in which the new overlaid area code was reserved for a particular type of service, such as cell phone and fax machine; while this is still generally done, it is now against Federal law to absolutely assign an area code for this) and "concentrated overlays" (in which some of the area retained a single area code, while the rest of the region received an overlay code).

After the remaining valid area codes were used up in expansion, in 1995 the rapid increase in the need for more area codes (both splits and overlays) forced NANPA to allow the digits 2~8 to be used as a middle digit in new area code assignments, with 9 being reserved as a "last resort" for potential future expansion. Area codes, or "number planning areas" ending in double digits, such as toll-free 800, 888, 877, and 866, personal 700 numbers, and high-toll 900 numbers, are reserved as Easily-recognizable codes (ERCs) and are not issued to actual areas. (Nevada was declined lucky 777 for this reason, however the Florida Space Coast area did get the 321 "countdown" area code as requested by Richard Cheshire [link].)

Splits and overlays

By 1995, many cities in the United States and Canada had more than one area code, either through splitting the city into different areas (splits) or having more than one area code for the same geographical area (overlays). For example, in Manhattan, New York, subscribers' numbers had the NPA code 212, but two additional codes—first 917 (which initially was exclusively for cell phones and faxes until struck down in a federal court), then 646—were also introduced. This means that the area code must be dialed, even for local calls. In other areas, 10-digit or 11-digit dialing is now required for all local calls. Atlanta, Georgia, was the first city in the United States to have mandatory 10-digit dialing throughout its metro area, roughly coinciding with the Olympic Games in Atlanta. At first, the new calling plan wasn't mandatory but was highly encouraged by television advertisements. After some time, though, it became mandatory to dial all 10 digits. Atlanta was used as the test case because at the time, it enjoyed the world's largest fiber optic bundle (equal to five times that of New York's), it was a big enough city without being too big, it has the largest local toll-free calling area in the world, and it is home to BellSouth, the Southeastern Regional Bell Operating Company.

The overlap between area codes and exchange prefixes has occasionally produced some confusion because the three digits can be the same for both. Nashua, New Hampshire, for example, has a local exchange that begins 888, which is also an area code for toll-free calls. If somebody in Nashua means to call 1-888-555-1212 but forgets the initial "1," he or she will actually dial the local number 1-603-888-5551. This, however, is generally not a problem in major metropolitan areas with overlapping area codes, which were mandated by the FCC to dial all ten digits for all local calls so as not to give new numbers or telecommunications providers a "disadvantage."

Expansion issues

Depending on the techniques used for area code expansion, the effect on telephone users varies. In areas in which overlays were used, this generally avoids the need for converting telephone numbers, so existing directories, business records, letterheads, and advertising can retain the same numbers, which the overlay is used for new number allocation. The primary impact on telephone users is the necessity of remembering and dialing 10- or 11-digit numbers when only 7-digit dialing was previously permissible.

The use of a split instead of an overlay generally avoids the requirement for mandatory area-code dialing, but at the expense of having to convert some of the numbers to the new area code. In addition to the requirements of updating records and directories to accommodate the new numbers, for efficient conversion this requires a period of "permissive dialing" in which both the new and old area codes of the split are allowed to work. Also, in many splits there were significant technical issues involved, especially when the area code splits occurred over different boundaries than the phone network divisions.

As an extreme example of a split, in 1998 the Twin Cities, which until that point used the 612 area code, split into the 612 and 651 codes, with St. Paul and the eastern metropolitan area receiving the new 651 code. However, the state Public Utility Commission mandated that the split boundary exactly follow town boundaries (which were distinctly different from telephone exchange boundaries), and that all subscribers keep their 7-digit numbers. These two goals were directly at odds with one another, and there were more than 40 exchanges whose prefix territory straddled town boundaries along the zone split. The result was prefixes duplicated in both area codes, which counteracted much of the benefit of the split, with only 200 of 700 prefixes in 612 moving entirely to 651. As a result, in less than two years the 612 area code again exhausted its number space, and underwent a 3-way split in 2000, creating the 763 and 952 area codes. Again, the split followed political boundaries rather than rate center boundaries, resulting in additional split prefixes, and in a few cases resulted in numbers initially moved to area 651 being moved again to the 763 code in less than two years.

Alphabetic mnemonic system

Another oddity of NANP telephone numbering is the popularity of alphabetic dialing. On most US and Canadian telephones, three letters appear on each number button from 2 through 9. This accommodates 24 letters. Historically, the letters Q and Z were omitted, though on some modern telephones, they are added, so that the alphabet is apportioned as follows:

2 = ABC
3 = DEF
4 = GHI
5 = JKL
6 = MNO
7 = P(Q)RS
8 = TUV
9 = WXY(Z)
No letters are allocated to the 1 or 0 keys (although some corporate voice mail systems are set up to count Q and Z as 1, and some old telephones assigned the Z to the digit 0).

Originally, this scheme was meant as a mnemonic device for telephone number prefixes. When telephone numbers in the US were standardized in the mid-20th century, they were made seven digits long, including a two-digit prefix, the latter expressed as letters rather than numbers. (Before World War II, many localities used three letters and four numbers, and in much of California during this period, phone numbers had only six digits — two letters followed by four numbers.) The prefix was a name, and the first two or three letters (usually shown in capitals) of the name were dialed. Later, the third letter (where previously used) was replaced by a number; this generally happened after World War II, although New York City did this in 1930. Thus, the famous Glenn Miller tune "PEnnsylvania 6-5000" refers to a telephone number 736-5000, the number of the Hotel Pennsylvania, which still bears the same number today. Similarly, the classic Elizabeth Taylor film "BUtterfield 8" refers to the section of New York City where the film is set, where the telephone prefixes include 288 (on the East Side of Manhattan between roughly 64th and 86th Streets). This is why, in some works of fiction, phone numbers will begin with "KLondike 5", which translates to 555, a mostly unused and reserved exchange.

Today this system has been abandoned (in fact it generally stopped by the mid-1970's), but alphabetic dialing remains as a commercial mnemonic gimmick, particularly when combined with toll-free numbers. For example, one can dial 1-800-FLOWERS to send flowers to someone. Sometimes, longer words are used - for example one might be invited to give money to a public radio station by dialing 1-866-KPBS-GIVE. The "number" is 8 digits long, but only the first seven need be dialed. If an eighth (or more) digit is dialed, the switching system will ignore it. Mobile users must manually drop any numbers past the seventh digit as mobile switching systems will not automatically ignore them, resulting in a failed call. In addition to commercial uses, alphabetic dialing still remains, in rare cases, in regional areas codes in the United States. For example, when East Tennessee was split into two area codes in 1999, the region surrounding Knoxville received a new code; the code 865 was chosen to represent the word "VOL"—short for "Volunteers", the nickname of athletic teams at the University of Tennessee.

Cellular services and the NANP numbering scheme

A difference between the NANP system and other plans is that apart from area code 600 in Canada, no separate, non-geographical area codes have been created for cellular phones, as is the case in most European and Asian countries, where mobile services are assigned their own prefixes. This means that most North American mobile phones are assigned the same locality-specific codes as landlines, and calls to them are billed at the same rate. Consequently, the caller-pays pricing model adopted in other countries, in which calls to cell phones are charged at a higher nationwide rate, but receiving calls is free, could not be used. Instead, North American cellphone users are also generally charged to receive calls as well (subscriber pays). In the past, this discouraged mobile users from using the phones or giving out the number. However, robust price competition among carriers has led to dramatic cuts in the average price per minute for contract customers (for both inbound and outbound calls), which can compare favorably to those in caller-pays countries. Most users select bundle pricing plans that include all the minutes they expect to use in a month, and many carriers offer first inbound minute free or in some cases, entirely free inbound calling.

Some industry observers have blamed user pays as one of the main factors in the relatively low penetration rate of mobile telephony in the United States compared to that of Europe. However, in the wireless-subscriber-pays model the convenience of the mobility inures to the subscriber, which many users regard as a fairer pricing system. Callers from outside the local-calling region of the assigned number are, however, forced to pay for a long-distance call, although domestic long distance rates are generally lower than the rates caller-pays systems charge (conversely, an advantage of caller-pays is the relative absence of telemarketing and nuisance calls to mobile numbers). The integrated numbering plan also enables local number portability between fixed and wireless services within a region, allowing users to switch to mobile service while keeping their phone number, which is not a common option in caller-pays systems.

The initial plan for overlays did allow for providing separate area codes for use by mobile phones, faxes, pagers, etc., although these were still assigned to a specific geographical area, rather than the nationwide mobile area codes common to most other countries, and were charged at the same rate as other area codes. Initially, the new 917 area code for New York City was specifically assigned for this purpose within the 5 boroughs; however a Federal court struck this down and banned the use of an area code for a specific telephony purpose. Since mobile telephony is expanding faster than landline, new area codes typically have a disproportionately large fraction of mobile numbers, although landline and other services rapidly follow and local network portability can blur these distinctions.

The experience of Hurricane Katrina and similar events revealed a possible disadvantage of the methods employed in the geographic assignment of cellular numbers. Many mobile phone users could not be reached, their phones rendered inoperable, even when they were far from the stricken areas, because the routing of calls to their phones depended on equipment in the affected area. A hypothetical caller-pays system with separate numbers would not have required geographical routing, although the existing system could have been designed to avoid this problem as well.

Another related issue for services like mobile telephony is the scarcity of telephone numbers. In contrast to other countries, where mobile and other special-number operators enjoy wide leeway to generate large numbers of telephone numbers, this is not an option in the NANP, with its geographical area codes with a fixed number of digits. Because of the scarcity of telephone numbers, the market value of each is consequently higher. This has been cited by mobile operators as another factor putting pressure on the development of cellular services, and of pay as you go in particular, although the decreasing rate at which new telephone numbers are being allocated suggests that other factors may be at work.

New area codes

Prior to 1995, all other NANP countries and territories outside the fifty United States and Canada, including Puerto Rico and the US Virgin Islands, shared the NPA code 809, but they are now able to have separate codes. Code (809) is now only used by the Dominican Republic. In 1997 the US Pacific Territories of the Northern Marianas and Guam became part of the NANP, as did American Samoa in October 2004.

Bermuda:

Puerto Rico:

US Virgin Islands:

Northern Marianas:

Guam:

American Samoa:

See also: Split from the 809 Area code

Fictional telephone numbers

In American television shows and films, 555 (or, in older movies and shows, KLondike 5 or KLamath 5) is used as the first three digits of fictional telephone numbers, so if anyone is tempted to telephone a number seen on screen, it does not cause a nuisance to any actual person. (A classic example of such a nuisance is the 1982 song 867-5309/Jenny by Tommy Tutone, which is still the cause of a large number of nuisance calls.) However, not all numbers beginning with "555" are fictional—for example, 555-1212 is the number for directory assistance in many places. In many, but not all areas, dialing "555" numbers other than 555-1212 will actually get you to directory assistance as well. 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. Some movies have started to use fictional telephone numbers starting with "1", giving someone a "telephone number" of 167-1402 in one film, for example.

Future expansion of NANP

The North American Numbering Plan Administration (NANPA) is now overseen by NeuStar Inc., which will face the task of adding at least one or two digits to the system within the next 25 years, likely before 2030. During that time, all public and private phone systems on the continent will have to be upgraded and reprogrammed (or even replaced) to recognize the new dialing rules.

The plans being considered now add a 1 or 0 to the end of the area code or the beginning of the local 7-digit number (or both), which will require mandatory 10-digit dialing (even for local calls) be in place everywhere, well before the transition period. In another proposal, existing codes may be changed to "x9xx" (e.g. San Francisco 415 would become 4915); once that conversion is complete, the new second digit would be opened for a new range. Other proposals include reallocating blocks of numbers assigned to smaller long distance carriers or unused reserved services.

Other vertical service codes, such as *69 (callback) and *70 (suspend call waiting), are also getting an extra digit, as have long-distance service provider codes such as 10-321 (now 10-10-321), all requiring the coordination of the NANPA.

Special numbers and codes

Some common special numbers in the North American system:

There are also special codes, such as:

Note: The four digit numbers do not work in some areas. The codes prefixed with the * symbol are intended for use on ® Touch-Tone telephones whereas the 4 digit numbers prefixed 11-- are intended for use on older rotary dial telephones where the ® Touch-Tone * symbol is not available.

Not all NANPA countries use the same codes. For example, the emergency telephone number is not always 911: Trinidad and Tobago uses 999, as in the United Kingdom.

Despite its importance as a share of the worldwide telephone system, few of the NANP's codes, such as 911, have been adopted outside the system. Most countries outside North America have chosen the International Telecommunication Union's 00 as their international access number; 112 is the standard emergency number in European Union alongside existing emergency numbers. Only the toll-free prefix 800 has been widely adopted elsewhere, including as the international toll-free number.

List of NANPA countries and territories

See also

External links

 

From Wikipedia, the Free Encyclopedia. Original article here. Support Wikipedia by contributing or donating.
All text is available under the terms of the GNU Free Documentation License See Wikipedia Copyrights for details.

Search Titles
0123456789
ABCDEFGHIJ
KLMNOPQRST
UVWXYZ?

E-mail this article to:

Personal Message: