Los Angeles see , , , NW Indiana: Gary see , split , Northern NE Illinois: SW Georgia: Oakland County split from ; see overlay S Alabama: South Tier - Tacoma, Federal Way split from , see also ; overlay Central Texas Waco, Stephenville; split, see , SE Wisconsin: SW Michigan: S and SW Virginia: S Cent. W Maryland: SE Florida: Miami, the Keys see , ; Chicago downtown only -- in the loop; see ; overlay SE Missouri: St Louis city and parts of the metro area only see , , overlay NE Ohio: W Washington State: Olympia, Bellingham except Seattle area; part of what used to be ; see overlay N central Florida: N Georgia: Atlanta and suburbs see overlay , split E Maryland: W Pennsylvania: Pittsburgh see split , overlay E Tennessee: Chattanooga, Bristol, Johnson City, Kingsport, Greeneville see split ; part of what used to be North Tier - Everett, Bellevue split from , see also ; overly E Virginia: SW Quebec: Cleveland metro area, excluding Cleveland split from , see also Central Georgia: NW Arkansas: East Phoenix see ; also Phoenix split , SE Pennsylvania: Framingham; Cape Cod see split , overlay S Texas: SW Ohio: Some of these combinations, however, are not available or have been reserved for special purposes.

Among them are the following: Easily Recognizable Codes When the second and third digits of an area code are the same, that code is called an easily recognizable code ERC. ERCs designate special services; e. N11 These 8 ERCs, called service codes, are not used as area codes. N9X The 80 codes in this format, called expansion codes, have been reserved for use during the period when the current digit NANP number format undergoes expansion. More about area codes Some of these combinations, however, are not available or have been reserved for special purposes Among them are the following: Easily Recognizable Codes.

The combination of NPA and central office code served as a destination routing code for use by operators and subscribers to reach any central office through the switching network. Due to this limitation, the most populous states required division into multiple NPAs. New York state was initially divided into five areas, the most of any state. Eight states and provinces were split into two NPAs. These divisions attempted to avoid cutting across heavy toll traffic routes, so that most toll traffic remained within an area, and outgoing traffic in one area would not be tributary to toll offices in an adjacent area.

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Traditionally, subscribers were assigned four-digit numbers, meaning that each central office could serve up to ten thousand subscriber numbers. Thus the new numbering plan identified each telephone in the system with the combination of area code, central office code, and line number, resulting in a closed telephone numbering plan with a ten-digit national telephone number for each telephone. The intent was for subscribers not to have to dial an area code when making a local call or a call within their plan area, resulting in seven-digit dialing.

Area codes were only required in ten-digit dialing when placing foreign area calls to subscribers in another state or numbering plan area. The new network design, completed in , provided for one hundred fifty-two area codes, each with a capacity to serve five hundred forty central offices. New Jersey received the first area code in the new system, area code The allocation of area codes was readjusted as early as to account for inadequacies in some metropolitan areas.

For example, Indiana area code was split to provide a larger number pool in the Indiana suburbs of Chicago area code Initially, states divided into multiple area codes were assigned area codes with a 1 in the second position, while areas that covered entire states or provinces received codes with 0 as the middle digit; however, this rule was abandoned by the early s. This was already common practice, because the system of using the initial letters of central office names did not assign letters to digits 1 and 0.

Furthermore, area codes and central office codes could not start with 0 or 1 , because 0 was used for operator assistance and a leading single pulse i. Additional area code patterns were later assigned for other services; for example, the area codes N10 were implemented for the Teletypewriter Exchange Service TWX. The central office code was chosen such that it could be represented by the first two letters of the central office name according to a digit-to-letter mapping that was printed on the face of a rotary dial, by grouping a set of letters with the digits 2 through 9. Such letter translations, designed by W.

Blauvelt in , had been used in the Bell System in large metropolitan areas since the late s.

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The original plan of had been projected to be usable beyond the year However, by the late s it became apparent that it would be outgrown by about In the late s and early s, the NANPA implemented calling procedures that required all long-distance calls within an area code to be prefixed with the area code, in an effort to make it possible to assign central-office prefixes with 0 or 1 in the middle position except for N11 , which would otherwise be wrongly taken by the local telephone switch to be the area code. As it had nearly run out of area codes using the existing assignment methods, this expanded the number pool for each area code by nearly twenty-five percent and also allowed for the later addition of area codes with middle digits other than 0 or 1.

Requiring a 1 to be dialed before the full number in some areas also provided for area codes of the form N10 , such as in the San Antonio , Texas, area and in eastern Maryland. Therefore, someone calling from San Jose, California , to Los Angeles before the change would have dialed and after the change , which permitted the use of as an exchange prefix in the San Jose area. For example, is a valid telephone number with area code , central office prefix exchange , and line number The number is invalid, because the central office code must not be in the form N The country calling code for all countries participating in the NANP is 1.

Each three-digit area code has a capacity of 7,, telephone numbers:. Various office codes in certain plan areas are deliberately not issued; for example, numbers xxxx , where and are both 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. Using 0 or 1 as 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; these are trunk prefixes or reserved for North American Numbering Plan expansion.

While the national numbering plan of the NANP was designed as a digit closed plan, international direct distance dialing IDDD was accomplished by extensive modifications in switching systems to accommodate an open international numbering plan for telephone numbers from seven to twelve digits. Canada and the United States have experienced rapid growth in the number of area codes, particularly between and The widespread adoption of fax , modem , and mobile phone communication, as well as the deregulation of local telecommunication services in the United States in the mids, increased the demand for telephone numbers.

The Federal Communications Commission allowed telecommunication companies to compete with the incumbent local exchange carriers for services, usually by forcing the existing sole service provider to lease infrastructure to other local providers. Because of the original design of the numbering plan and the telephone switching network that assumed only a single provider, number allocations had to be made in 10,number blocks even when much fewer numbers were required for each new vendor.

Due to the proliferation of service providers in some numbering plan areas, many area codes fell into jeopardy , facing exhaustion of numbering resources.

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The number blocks of failed service providers often remained unused, as no regulatory mechanism existed to reclaim and reassign these numbers. Area codes are added by two principal methods, number plan area splits and overlay plans. Splits were implemented by dividing an area into two or more regions, one of which retained the existing area code and the other areas receiving a new code. In an overlay, multiple codes are assigned to the same geographical area, obviating the need for renumbering of existing services.

Subtle variations of these techniques have been used as well, such as dedicated overlays , in which the new code is reserved for a particular type of service, such as cellular phones and pagers, and concentrated overlays , in which a part of the area retained a single code while the rest of the region received an overlay code. The only service-specific overlay in the NANP was area code New York City when it was first installed; such service-specific area code assignments were later prohibited by the Federal Communications Commission.

The last of these, , was assigned to Canada, but reassigned in These new area codes, as well as a few other codes used for routing calls to Mexico, were used for telephone area code splits in the late s and early s, as all other area codes under the original plan had been consumed. After the remaining valid area codes were used up by expansion, in the rapid increase in the need for more area codes forced the 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 in Alabama and area code in Washington, which both began service on January 15, This was quickly followed by area code serving Arizona on March 19, Codes ending in double digits are reserved as easily recognizable codes ERCs , to be used for special purposes such as toll-free numbers, personal numbers, Canadian non-geographic area code , carrier-specific numbers, and high-toll numbers , rather than for geographic areas.

Nevada was denied "lucky 7s", a reference to the state's legalized gambling for this reason; [26] it received instead when most of Nevada split from , which continues to serve the Las Vegas metropolitan area. By , 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 , but two additional codes—first which initially was exclusively for cellular phones and pagers until that idea was struck down in a Federal court [ citation needed ] , then —were also introduced.

This means that the area code must be dialed, even for local calls.

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In other areas, digit or digit dialing is now required for all local calls. The transition to digit dialing typically starts with a permissive dialing phase in which 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 U.

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 or digit numbers when only 7-digit dialing was previously permissible. Splitting instead of overlaying generally avoids the requirement for mandatory area-code dialing, but at the expense of having to convert a region 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. In area code , which had covered the Minneapolis — Saint Paul Twin Cities, was split to create area code 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, namely to provide additional phone numbers. More than 40 exchanges had territory that straddled the new boundary.

As a result, prefixes were duplicated in both area codes, which counteracted much of the benefit of the splitting, with only of prefixes in area moving entirely to area In less than two years area code again exhausted its supply of phone numbers, and required a three-way split in , creating the new area codes and Again, the split followed political boundaries rather than rate center boundaries, resulting in additional split prefixes; a few numbers moved from to and then to in less than two years. Recognizing that the proliferation of area codes was largely due to the telecom regulation act and the assignment of numbers in blocks of 10,, the FCC instructed NANPA, by then administered by Neustar , to alleviate the numbering shortage.

As a result, number pooling was piloted in as a system for allocating local numbers to carriers in blocks of 1, rather than 10, Because of the then design of the switched telephone network, this was a considerable technical obstacle. Number pooling was implemented with another technical obstacle, local number portability.

The program has been implemented in much of the United States by state regulators. A limited number of cities have also implemented rate center consolidation; fewer rate centers resulted in more efficient use of numbers, as carriers would reserve blocks of 1, or 10, numbers in each of multiple rate centers in the same area even if they had relatively few clients in the area. Typically a call within a rate center is local, while a call from one rate center to another is a long-distance call.

Together with aggressive reclamation of unused number blocks from telecom providers, number pooling has reduced the need for additional area codes, so that many previously designated area splits and overlays have been postponed indefinitely. There is no number pooling in Canada. Number allocation remains highly inefficient as even the tiniest village is a rate center and every CLEC is assigned blocks of ten thousand numbers in every place it offers new local service. As a result, dialing seven digits even in remote locations like James Bay is more likely to produce an intercept message " dial the area code " than an actual voice connection.

This included Puerto Rico and the U. Virgin Islands. Each has since been assigned one or more distinct numbering plan areas; area code now exclusively serves the Dominican Republic along with area codes and The NANP exhaust analysis estimates that the existing numbering system is sufficient until , based on the assumption that a maximum of NPAs continue to be available and that on the average central office codes are needed per year.

In case of exhaustion, various plans are discussed for expanding the numbering plan. One option is to add the digit 1 or 0 either at the beginning or at the end of the area code , or prefixing it to the seven-digit subscriber number.