North American Numbering Plan |
The North American Numbering Plan is a system for three-digit area codes that direct telephone calls to particular regions on a
public switched 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. Despite the "North American" name, Mexico and the
Central American countries are not part of the system, although direct dialing from the NANP to some parts of Mexico continued
until 1991.
However, calls between different countries and territories that use the NANP are not charged as domestic. Calls
between the US and Canada are generally treated as international, although charged at much lower rates than calls to other
countries. Call costs to other destinations in the NANP area can be even higher- for example, it 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.
Some common special numbers in the North American system:
0 - operator assist
00 - Long Distance Operator Assist
011 - International access code (for all destinations outside NANP)
10x xxxx - used to indicate use of an alternative long distance service
211 - social services (in some cities)
311 - non-emergency police matters (in some cities)
411 - local directory service
511 - traffic, road, and tourist information (in some cities and states)
611 - telephone line repair service
711 - relay service for hearing-impaired or mute customers
811 - telephone company services
911 - emergency dispatcher for fire, ambulance, police etc.
(area code) 555-1212 - non-local directory service.
There are also special codes, such as:
*70 Cancel call waiting
*67 Caller ID Block
*69 Call Return caller may press '1' to return call after hearing number
*82 releases Caller ID on a call-by-call basis
Not all NANPA countries use the same codes. The emergency telephone number is often different from country to country. For example, Trinidad and Tobago uses 999, as in the United Kingdom.
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. 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 (a total of 5 clicks, 2+1+2), Los Angeles given 213, and Chicago 312, while Vermont received 802 (a total of 20 clicks, 8+10+2).
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 numbers in northwest Mexico
and Mexico City before 1991:
1 905 xxx xxxx (Mexico City)
1 706 xxx xxxx (northwest Mexico)
From that year, this was discontinued in favour of the international format:
011 52 5 xxx xxxx (Mexico City)
011 52 6 xxx xxxx (northwest Mexico)
Expansion in 1995
The continuing increase in the need for more area codes (both splits and overlays) forced NANPA to allow the digits 2~8 to be
used 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.)
Splits and overlays
As of 1995, many cities in the US and Canada now had more than one area code, either
through splitting the city into different areas ('splits'), or more than one 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, 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.
7-digit dialing: xxx xxxx (NPA code not required)
10-digit dialing: NPA xxx xxxx
11-digit dialing: 1 NPA xxx xxx
The overlap between area codes and exchanges 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"
they will actually dial the local number 888-5551. This however is generally not a problem in major metropolitan areas with overlapping area codes, which were mandated to
dial all ten digits for all locals calls by the FCC so as not to give new numbers a "disadvantage".
New area codes
Prior to 1995, all other countries and territories outside the US and Canada, including Puerto Rico and the US Virgin Islands shared
the NPA code 809, but were now able to have separate codes.
Until 1995: +1 809 29x xxxx
After 1995: +1 441 xxx xxxx
Until 1995: +1 809 xxx xxxx
After 1995: +1 787 xxx xxxx
Until 1995: +1 809 xxx xxxx
After 1995: +1 340 xxx xxxx
The NPA 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, thereby being rated as domestic long distance from the US: (American Samoa is to follow suit in 2004.)
Until 1997: +670 xxx xxxx
After 1997: +1 670 xxx xxxx
Until 1997: +671 xxx xxxx
After 1997: +1 671 xxx xxxx
Until October 1, 2004: +684 xxx xxxx
Starting October 2, 2004: +1 684 xxx xxxx
Fictional Telephone Numbers
In TV shows and movies originating
in the USA, 555
(or very rarely, KLondike 5 or KLamath 5) is used as the first three digits of fictional
telephone numbers so that if anyone is tempted to telephone a
number seen on screen, it does not cause a nuisance to any actual person. However, not all numbers that begin with "555" are fictional--for example, 555-1212 is the
number for directory assistance in many places. 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 gone to creating fictional telephone numbers starting with "1", giving someone a "telephone
number" of 167-1402 in the film, for example.
Future Expansion of NANP
The North American Numbering Plan Administration (NANPA) is now overseen by the private company NeuStar Inc., who 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 "a9bc" (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 NANPA.
List of NANPA countries and territories
External links
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