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The North American Numbering Plan (NANP) is an integrated telephone numbering plan administered by NeuStar (formerly Lockheed Martin IMS) which encompasses 24 countries and territories, including the United States and its territories, Canada, Bermuda, and 17 nations of the Caribbean. The term is also used, by metonymy, to refer to the geographic area in which that plan has been implemented.
The NANP is a standardized system of numbering plan areas (NPA), which have evolved over time into a system of three-digit area codes and seven-digit telephone numbers. Through this plan, telephone calls can be directed to particular regions of the larger NANP public switched telephone network (PSTN), where they are further routed by the local networks.
Developed in the 1940s, and first implemented in 1951 by AT&T, the NANP set out to simplify and facilitate direct dialing of long distance calls. Area code 201 was the first implemented under the plan. The NANP initially applied only to the U.S. and Canada, but at the request of the British Colonial Office, it was expanded to Bermuda and the British West Indies (including Trinidad and Tobago), because of their historic telecommunications administration through Canada as parts of the British Empire — and also their continued associations with Canada, especially during the years of the telegraph and the All Red Line system.
Despite the "North American" name of the calling plan, not all North American countries participate in NANP. Mexico, the Central American countries and some Caribbean countries (Cuba, Haiti, and the French and Dutch-speaking Caribbean, though Dutch-speaking Sint Maarten joined the NANP in September 2011) are not part of the system. The only Spanish-speaking sovereign nation in this plan is the Dominican Republic. Mexican participation was planned, but implementation stopped after two area codes were put into use (Mexico City and northwestern Mexico); these ended in 1991 when Mexico withdrew from the NANP.
Saint Pierre and Miquelon (+508) and Greenland (+299), both North American possessions of European Union nations, use non-NANP codes which are independent of their respective home countries (+33 France and +45 Denmark).
The NANP is administered by the North American Numbering Plan Administration (NANPA).
Current NANP number format can be summed up via the following:
The country calling code for the NANP is +1. In international format, an NANP number should be listed thus: +1 301 555 0100 (example using the original area code for Maryland). "1" is also the code often used to make direct-dialed long-distance calls within the NANP.
Each three-digit area code may contain up to 7,919,900 unique phone numbers:
Dialing plans vary from place to place depending on whether an area has overlays (multiple 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.
Most areas allow permissive dialing of 10D or 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 when there is no toll alerting. Allowing 7D local dialing across an area code boundary (which is uncommon today and only possible with toll alerting) requires NXX protection on the other side to avoid dialing conflicts.
Most areas permit local calls to be dialed as 1+10D except for Texas, Georgia, and some jurisdictions in Canada which require that landline callers know which numbers are local and which are toll, dialing 10D for all local calls and 1+10D for all toll calls.
In almost all cases, operator-assisted calls require dialing 0+10D.
Despite the similar dialing format, calls between different countries and territories that use the NANP are not necessarily charged as domestic. Calls between the US and Canada are treated as international, excluding them from some flat-rate long-distance plans, but are 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 as the domestic format. 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 by directly charging heavier pricing levies on the international Long Distance services.
Because of these higher fees, a handful of scams had taken advantage of customers' unfamiliarity with pricing structure to call the legacy regional area code 809. Some scams lured customers from the U.S. and Canada into placing expensive calls to the Caribbean, by representing area code 809 as a regular domestic, low-cost, or toll-free call. The split of 809 (which formerly covered all of the Caribbean NANP points) into multiple new area codes created many new, unfamiliar prefixes which could be inadvertently mistaken for US or Canada domestic area codes but carried high tariffs. In various island nations, premium exchanges such as +1-876-HOT-, +1-876-WET- or +1-876-SEX- (where 876 is Jamaica) became a means to circumvent consumer-protection laws governing area code 900 or similar US-domestic premium numbers.
These scams are currently on the decline, with many of the Cable and Wireless service monopolies being opened up to competition, hence bringing rates down. Additionally, many Caribbean territories have implemented local government agencies to regulate telecommunications rates of providers.
In order to facilitate direct dialing calls, the NANP was created and instituted in 1947 by AT&T, also known as the Bell System, the U.S. telephone semi-monopoly. At first, the codes were used only by long-distance operators; the first customer-dialed calls using area codes did not occur until November 10, 1951, when the first directly dialed call was made from Englewood, New Jersey to Alameda, California. Direct dialing was gradually instituted throughout the country, and by the mid-1960s, it was commonplace in most larger cities.
Originally there were only 86 codes, with the biggest population areas getting the numbers that took the shortest time to dial on rotary telephones. Thus, five largest cities based on 1950 US Census population: New York City was given 212, Chicago 312, Philadelphia 215, Los Angeles 213, Detroit 313; while four areas received the then-maximum number of 21 clicks: South Dakota (605), North Carolina (704), South Carolina (803), and the Maritime Provinces of Canada (902). Additionally, in the original plan a middle digit of 0 indicated that the area code covered an entire state/province, while area codes with a middle digit of 1 were assigned to jurisdictions that were divided into multiple area codes. 
At first, area codes were all in the form NYX, where N is any number 2–9, Y is 0 or 1, and X is any number 1–9 (if Y is 0) or any number 2–9 (if Y is 1). 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" (with 0 or 1 as the second digit) and the three-digit "exchange" prefix (which had avoided 0 or 1 for the second digit, because of restrictions in existing switching equipment). For example, when a caller dialed "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 345-6789, the 4 would cause the number to be recognized as a long-distance number within the area and routed as such, without waiting for the caller to finish dialing.
In the late 1980s and early 1990s, NANPA (then still part of Bellcore, which is now Telcordia Technologies) began to urge and later require all long-distance calls within each area to be prefixed with the digit 1 to distinguish them from local calls, so that badly needed prefixes with 0 or 1 in the middle could be assigned to local telephone exchanges. Also, since it had nearly run out of area codes using the above formula, it allowed the assignment of area codes using the form N10, such as 210 in the San Antonio, Texas, area and 410 in eastern Maryland. Therefore, someone calling from San Jose to Los Angeles before the change would have dialed 213-555-1234 and after the change 1-213-555-1234, which then allowed 213 to be used as an exchange prefix in the San Jose area.
Until 1991, calls to some areas of Mexico from the United States and Canada were made using NANP area codes, but Mexican participation in the NANP was discontinued in favor of the general international format, using country code +52 instead. Area Code 905 (formerly Mexico City) was re-assigned to the Greater Toronto Area outside of Toronto (which retained Area Code 416), and Area Code 706 (formerly northwest Mexico) was reassigned to northern Georgia, surrounding the Atlanta region which retained 404.
Canada and the United States have experienced rapid growth in the number of area codes, particularly between 1990 and 2005. There are two main reasons for this. First, there is the increasing demand for telephone services (particularly resulting from widescale adoption of fax, modem, and mobile phone communications).
The second and more important reason is the telecom deregulation of local telephone service in the US beginning in the early-to-mid 1990s. At that time, the Federal Communications Commission began allowing telecommunication companies to compete with the incumbent local exchange carrier (usually by forcing the existing monopoly service provider to lease infrastructure to other local providers who then resold the service to consumers). However, because of the original design of the numbering plan and telephone switching network that assumed only a single provider, number allocations had to be made in 10,000-number blocks.
Thus, whenever a new local service provider entered a given market, it would be allocated 10,000 numbers by default, even if the provider only obtained a few customers. As more companies began requesting numbering allocations, this caused many area codes to begin exhausting their supply of available numbers (code "in jeopardy" in telecom jargon), and additional area codes were needed. In reality, many of the new telecom ventures were not successful; while the number of area codes started increasing rapidly, this did not necessarily translate to a much larger number of actual telephone subscribers as large blocks of numbers lay unassigned to any "real" subscribers because of the 10,000-number block allocation requirement. When these telecom ventures were merged or bought or liquidated, their blocks went to the successor or went unused. No regulatory mechanism existed to reclaim and reassign these underutilized blocks.
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 area(s) receiving a new code), or "overlays", in which multiple codes are 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 code was reserved for a particular type of service, such as cellular phones and pagers (the only true example of this was area code 917 in New York City), and "concentrated overlays", in which a part of the area retained a single code while the rest of the region received an overlay code.
After the remaining valid area codes were used up by expansion, in 1995 the rapid increase in the need for more area codes (both splits and overlays) forced NANPA to allow the digits 2 through 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. At the same time, local exchanges were allowed to use 1 or 0 as a middle digit. The first area codes without a 1 or 0 as the middle digit were area code 334 in Alabama and area code 360 in Washington, which both began service on January 15, 1995.
Codes ending in double digits are reserved as easily recognizable codes (ERCs), to be used for special purposes such as toll-free 800, 888, 877, 866 and 855, personal 700 numbers, and high-toll 900 numbers, rather than for geographic areas. (Nevada was denied 777 for this reason; it received 775 instead when most of Nevada split from 702, which continues to serve the Las Vegas area.)
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 code for the same area (overlays). For example, in Manhattan, subscribers' numbers had the NPA code 212, but two additional codes—first 917 (which initially was exclusively for cellular phones and pagers until that idea was 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. The transition to 10-digit dialing typically starts with a permissive dialing phase in which both 7-digit and 10-digit dialing is optional. During this period, the transition is heavily publicized. After a period of several months, the mandatory dialing phase is introduced, in which 7-digit dialing no longer works. Atlanta was the first US city to have mandatory 10-digit dialing throughout its metropolitan area, roughly coinciding with the 1996 Summer Olympics held there. Atlanta was used as the test case not only because of its size, but also because it enjoyed the world's largest fiber optic network at the time (five times that of New York then), and it was home to BellSouth (now part of AT&T), then 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 with (603) 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."
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, business cards, advertising, and "speed-dialing" settings can retain the same phone numbers, while the overlay is used for new number allocations. 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 splitting 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 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 the new and old codes are both allowed to work. Also, many splittings involved significant technical issues, especially when the area splittings occurred over boundaries other than phone network divisions.
As an extreme example of an area code splitting gone somewhat awry, in 1998 area code 612, which had covered the Minneapolis – Saint Paul Twin Cities, was split to create area code 651 for St. Paul and the eastern metropolitan area. The Minnesota Public Utilities Commission mandated that the new boundary exactly follow municipal 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 the reason for the split (to generate additional phone numbers), and there were more than 40 exchanges whose territory straddled the new boundary. The result was prefixes duplicated in both area codes, which counteracted much of the benefit of the splitting, with only 200 of 700 prefixes in area 612 moving entirely to area 651. As a result, in less than two years area code 612 again exhausted its supply of phone numbers, and it underwent another three-way split in 2000, creating the new area codes 763 and 952. Again, the split followed political boundaries rather than rate center boundaries, resulting in additional split prefixes; a few numbers moved from 612 to 651 and then to 763 in less than two years.
Recognizing that the proliferation of area codes was largely due to the telecom deregulation act and the assignment of numbers in blocks of 10,000, the FCC instructed NANPA (by then administered by NeuStar) to look for a way to alleviate the numbering shortage. As a result a new program called "number pooling" was piloted in 2001, which allowed allocating numbers in blocks of 1,000 rather than 10,000. Because of the design of the switched telephone network, this was a considerable technical challenge and was carried out together with another technically challenging program, local number portability. Since then the program has been rolled out to most parts of the United States and, together with aggressive reclamation of unused number blocks from telecom providers, has reduced the need for additional area codes, so much so that many previously designated area splits and overlays have been postponed indefinitely.
Another oddity of NANP telephone numbering is the use of alphabetic dialing. On most US and Canadian telephones, three letters appear on each number button from 2 through 9 (as standardized much later by ISO 9995-8 and, in Europe, E.161). 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:
No letters are allocated to the 1 or 0 keys (although some corporate voicemail 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, with the first two digits, the prefix, expressed as letters rather than numbers. (Before World War II, a few localities used three letters and four numbers; in most cities with customer dialing, 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, or an extra number was added; 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 +1 (212) 736-5000, the number of the Hotel Pennsylvania, which still bears the same number today. Similarly, the classic film "BUtterfield 8" is set in the East Side of Manhattan between roughly 64th and 86th Streets, where the telephone prefixes include 288. This is why, in some works of fiction, phone numbers will begin with "KLondike 5" or "KLamath 5", which translates to 555, an exchange that is reserved for information numbers in most areas.
The letter system was phased out, beginning before 1965 (though it persisted ten years later in some places, and was included in Bell of Pennsylvania directories until 1983), but alphabetic dialing remains as a commercial mnemonic gimmick, particularly for toll-free numbers. For example, one can dial 1-800-FLOWERS to send flowers to someone, or 1-800-DENTIST to find a local dentist. Sometimes, longer phonewords 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 and VoIP users may need to manually drop any numbers past the seventh digit as some mobile switching systems will not automatically ignore them, resulting in a failed call. Also, some users of smartphones devices can have difficulty dialing phonewords, as some of those devices do not have the apportioned letters on the keys used for dialing. This can be avoided by accompanying the use of phonewords with the actual numeric phone number, allowing users of such smartphones to dial using the numeric phone number. Some smartphone permit dialing phonewords by holding down a special function key, such as ALT in the case of the BlackBerry, while pressing another key on the qwerty pad.
In addition to commercial uses, alphabetic dialing has occasionally influenced the choice of regional area codes in the United States. For example, when area 423 (East Tennessee) was split in 1999, the region surrounding Knoxville was assigned area code 865, chosen to represent the word "VOL"—short for "Volunteers", the nickname of athletic teams at the University of Tennessee.
The state of Nevada has previously attempted to obtain area code 777 (lucky 7's), but was unable to secure it.
A difference between the NANP system and other plans is that, apart from an obscure, rarely-used 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 cellular phones are charged at a higher nationwide rate but receiving calls is free, could not be used. Instead, North American cellular telephone 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. Many carriers also offer free calling between mobile phones on the carrier's network, and some also offer free calling to a list of user-selected phone numbers (which can include both cell phones and landlines).
Some industry observers have blamed "subscriber pays" as one of the main factors in the relatively low mobile phone penetration rate in the United States compared to that of Europe. In this model the convenience of the mobility is charged to the subscriber. Callers from outside the local-calling region of the assigned number, however, pay for a long-distance call, although domestic long distance rates are generally lower than the rates in caller-pays systems. 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.
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 area code 917 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.
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 quantities of telephone numbers, this is not an option in the NANP, with its geographical area codes with a fixed number of digits.
Prior to 1995, all other NANP countries and territories outside the fifty United States and Canada, including Puerto Rico and the U.S. 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 United States Pacific Territories of the Northern Mariana Islands and Guam became part of the NANP, as did American Samoa in October 2004. The Dutch possession of Sint Maarten was originally scheduled to join the NANP on May 31, 2010, but the changeover was postponed to September 30, 2011.
US Virgin Islands:
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.
There are occasions, however, when a non-555 is used in real-life context (often in songs), with varying intents and consequences. A classic example is the 1982 song "867-5309/Jenny" by Tommy Tutone, which is still the cause of a large number of nuisance calls, although an Indianapolis plumbing company used both the tune and the number for advertising purposes.
Similarly, 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 reserved for fictional use, with the other numbers having been released for assignment. Where used, these are normally information numbers; Bell Canada and BCTel had briefly promoted 555-1313 as a pay-per-use "name that number" reverse lookup in the mid-1990s. Since "1xx" exchanges are generally not assigned, some movies have started to use fictional telephone numbers starting with "1".
There are various numbers which are deliberately not issued (for instance, numbers like +1-212-718-xxxx, where 212 and 718 are both existing or proposed New York City area codes, are typically avoided to prevent confusion between an area code and a similarly-numbered local exchange in the same region). 958-xxxx and 959-xxxx are very commonly reserved for plant test (local and long distance, respectively); a few area codes once reserved additional test exchanges such as 999-xxxx, although this usage is declining. Area codes where the last two digits match are reserved for non-geographic numbers such as +1-800 or +1-888; if there is little or nothing in area code 500, there is no immediate probability of new non-geographic prefixes in the same range (such as +1-555) being created. A 0 or 1 in the first digit of an area code or seven-digit local number is invalid, as is a 9 as the middle digit of an area code. Lists of exchanges in an individual area code (posted by CNAC in Canada, NANP in the US) all list various specific reserved prefixes as deliberately not issued. Unlike the 555 exchange, many of these see little or no use as fictional telephone numbers.
The North American Numbering Plan Administration (NANPA) is now overseen by NeuStar, which will probably face the task of adding one or two digits to each number, likely sometime after 2038. During that time, all public and private phone systems within the NANP area will have to be upgraded and reprogrammed (or even replaced) to recognize the new dialing rules.
One plan being considered adds a 1 or 0 either to the beginning or end of the area code, or the beginning of the local 7-digit number (or both), which will require mandatory 11-digit dialing (even for local calls), between any two NANP numbers, well before the transition period. In another proposal, existing codes would be changed to "x9xx" (e.g. San Francisco's 415 would become 4915); once that conversion is complete, the new second digit would be opened for a new range. (Compare PhONE Day in the United Kingdom, which added a "1" to the beginning of area codes in preparation for later using other digits, such as "2", for new area codes.) Other proposals include reallocating blocks of numbers assigned to smaller long distance carriers or unused reserved services.
NANPA previously coordinated an expansion of long-distance carrier access ("dial-around") codes from five digits (such as 10-321) to seven (10-10-321), in 1998. Vertical service codes, such as *69 (callback) and *70 (suspend call waiting), have been designed to allow the use of both two- and three-digit codes.
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