Countries in World Zone 1
World Zone 1 comprises those countries whose telephone number system forms part of the North American Number Plan (NANP)
- United States of America
- CNMI (Confederation of North Mariana Islands)
- American Samoa
- The Countries and Islands in the Caribbean (excluding Cuba and Haiti)
Some telecom providers consider Alaska and Hawaii to be separate administrations (not part of the United States) for billing and international settlement purposes.
All the World Zone 1 countries have telephone numbers based on the North American Number Plan, in the form 1 Nxx Nxx xxxx. The initial "1" is normally only shown in international dialling lists.
In the tables on this site, 1212 and 1613 (the most commonly dialled NPA codes in the years up to 1970) are used as hypothetical Country Codes for USA and Canada respectively. Tables are provided to determine the Country from the NPA.
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NPA Codes and the North American Number Plan
The following paragraphs are based on information available at http://www.nanpa.com. NANPA administers the allocation of NPAs.
The NANP is the numbering plan for the Public Switched Telephone Network in Canada, the United States and its territories, and many Caribbean nations. (See list of Zone 1 Countries). It was invented in 1947 by AT&T and Bell Laboratories, and conforms with the International Telecommunications Union (ITU) Recommendation E.164, the international standard for numbering plans.
The area served by the North American Numbering Plan is divided into smaller areas, each identified by a three-digit Numbering Plan Area (NPA) code, commonly called an area code. The format of an NPA code is Nxx, where N is any digit 2 - 9, and x is any digit 0 - 9. Prior to 1995, the middle digit of an NPA code had to be "0" or "1". With the introduction of "interchangeable" NPA codes, this restriction was removed, greatly expanding the supply of available codes.
There are 800 possible combinations associated with the Nxx format. Some of these combinations, however, are not available or have been reserved for special purposes.
Full NANP numbers are ten digits in length, in the format: NPA Nxx xxxx where:
- NPA is as described above.
- The second three digits (Nxx) are called the central office code or prefix: N is any digit between 2 and 9, and x is any digit between 0 and 9.
- The final four digits, taking any value between 0000 and 9999, form the line number.
Full details regarding the NANP are available at www.nanpa.com/
As the demand for new telephone lines and numbers increases, so more of the available codes are being brought into service - see New NPAS for a list of forthcoming changes, and New NPAS - History, which includes those introduced since 1995.
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Not every three digit code is available for telephone area codes - some are reserved for future purposes; others are used for non-geographic purposes, such as emergency services, Directory Enquiries, Audio-text services, etc. Some examples of excluded codes are: (this is not a complete list)
N - any digit from 2 to 9
x - any digit from 0 to 9
ERC - Easily Remembered Code
|1xx||Not used, since "1" is the access code for Long Distance and/or International in some states.
|37x, 96x||Reserved for future use, where a contiguous block of codes may be needed.|
|N9x||Reserved for use when 10 digits are insufficient, and the number length is expanded.|
|Nxx, where xx are repeated digits from 0 to 9. e.g. 233, 544, 688||Easily Remembered Code (ERC). ERCs are used to designate special services.|
|N11||Access to services, e.g. emergency services (911), non-emergency services (311), Directory Enquiries (411)|
|800, 855, 866, 877, 888||ERCs used for Toll Free services|
|900||ERC used for Audio-text and Premium Rate services|
|555||Not in general use, though often quoted in films. Some service numbers have been allocated on this level.
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Caribbean Code Changes
Up until 1995 all codes used in the Caribbean were of the form 809 Nxx xxxx. Since 1995 the codes have been gradually changed to NPA format (the changeover being completed in May 1999).
This means that numbers of the form 809 Nxx xxxx (except Dominican Republic numbers) have changed to NPA Nxx xxxx.
The changes allow the individual countries to expand their available number ranges considerably. For example, all numbers in Puerto Rico changed from 809 Nxx xxxx to 787 Nxx xxxx, allowing Puerto Rico to use all the 800 (approx.) useable
Central Office Codes between 787 201 xxxx up to 787 998 xxxx. [Puerto Rico has now almost run out of available numbers in the 787 range; a new NPA (939) was introduced in August, 2001 - see item ]
Dominican Republic retains 809 as an NPA and will expand its number base to use the whole 809 Nxx xxxx number range. As the range fills, a new code (829) has been introduced (August 2005) to cater for further expansion.
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Over the years some USA dependencies and other countries in Atlantic and Pacific oceans have obtained NPA codes. Among these are:
- American Samoa (2004)
- CNMI (Confederation of North Mariana Islands) (1997)
- Guam (1997)
- Sint Maarten (proposed for 2010)