An area code is a set of three digits that starts a North American phone number. It denotes a service area which is usually a geographical region with phone subscribers. This is also known as a numbering plan area (NPA). Each NPA is assigned a unique area code.
Area codes were introduced with the North American Numbering Plan (NANP) to make it easier to route calls. These digits serve as designation routing addresses or identifiers in public switched telephone networks (PSTNs). Each state in the United States has at least one area code. California has the highest number of area codes, followed by Texas, Florida, and New York.
Area codes are not assigned by land mass or state size. Rather, they are assigned by the number of phone users in a particular region. Each area code can provision 7,919,900 phone numbers. When a state, city, or metropolitan area is projected to have more than this number of phone subscribers, a new area code is created to accommodate users as more phone numbers are added.
A Brief History of the NANP
Before the introduction of the North American Numbering Plan (NANP), there were different phone numbering plans in North America. These systems were conflicting, and long-distance calls were difficult to route successfully. In the 1940s, AT&T developed and introduced the NANP to unify local numbering plans into a single system recognized by all participating countries.
AT&T managed the NANP until the breakup of its parent company, Bell System. Thereafter, the administration of the unified numbering system went to the North American Numbering Plan Administrator (NANPA) under the oversight of the Federal Communications Commission (FCC). The FCC only administers the NANP in the US. Other participating countries have their own regulatory bodies overseeing the allocation of new area codes in their regions.
Both Canada and the United States use the NANP, as well as Caribbean countries. In all, 20 countries use this unified system. Some North American countries do not participate in NANP. Mexico is a prominent example of such countries.
Are Area Codes Different from Prefix Codes?
Yes. Prefix codes are also known as central office codes. A prefix code is the first set of three digits in a seven-digit North American phone number. It comes after an area code if the phone number is written fully as a 10-digit set. In this phone number, (234) 289-1234, the area code is 234, while the prefix code is 289. The last four digits (1234) make up the line number. This last sequence of numbers is unique to each phone user.
When calling a North American phone number from a country besides those participating in the NANP, the caller must add a country calling code. Countries participating in the NANP have the same international calling code of 1. Therefore, the international format of the fictitious US (as well as participating countries) referenced above is +1 (234) 289-1234.
What Is a Central Office Code?
A central office code denotes a specific exchange within the switching network serving the locations covered by an area code. As designed by the NANP, each area code can have a maximum of 540 central offices.
The combination of area and prefix codes provides a complete destination address for phone operators routing calls through a PSTN. Both area and prefix codes point to the geographic location of a given number. While an area code establishes its broad location, a prefix code narrows down the location further and can pinpoint the section of a city or neighborhood where the phone number was assigned.
When dialing another number with the same area code, the user only needs to provide the central office code and line/subscriber number. However, a call to another area code requires providing the recipient's or destination area code to successfully route.
Are Area and Prefix Code Numbers Randomly Assigned?
No. The NANP assigns area and prefix codes by a set of rules. The general notation for phone numbers assigned in North American countries participating in the NANP is NPA-NXX-XXX. NPA represents the numbering plan area or area code, while NXX represents the prefix code or central office code. XXXX is the four-digit line number that is unique to each subscriber.
The first digit of the NPA is restricted to 2 - 9. This means that the first digit of an area code cannot be 0 or 1. The second and third digits of this code can be any number from 0 - 9. However, the NANP currently avoids assigning 9 to the second digit. Therefore, area codes with 9 in the second digit are invalid.
When the second and third digits of an area code are the same, then the area code is referred to as an ERC or easily recognized code. ERCs are reserved for special services and are not given to regular phone subscribers. Examples of ERCs are 800 for toll-free services and 911 for emergency services.
The same numbering rules apply to prefix codes. The first digit can only be a number from 2 to 9, while the acceptable range for both second and third digits is 0 - 9. However, the third digit of a central office code cannot be 1 if the second digit is also 1. This is to prevent the creation of a 911 prefix code which may be confusing to callers trying to reach emergency services.
Each of the four digits of a line number can be any number from 0 to 9. With a subscriber number, all combinations of digits are allowed. For most area codes, however, some potentially valid prefix codes are left unassigned. This omission typically happens when the:
- Prefix code and other area codes are the same, e.g., (235) 235-XXXX
- Area codes are for nearby communities
- Area codes are reserved for future expansion
- Area codes are used for industry testing such as 958 and 959, local and long-distance codes used by telephone installers to test individual lines
- Area codes are used for special services like 950 for carrier access from non-subscriber locations
What Is an Area Code Overlay?
An overlay plan occurs when multiple area codes are assigned to the same geographic area. With this arrangement, an NPA has one or more area codes in addition to the one originally assigned to the area. This occurs when the original area code and its prefix codes are close to exhausted as more phone users live in the area.
Therefore, overlay codes are area codes created to accommodate more phone users and unlock more phone numbers for a specific area. These codes are common in urban areas experiencing rapid growth. According to the US Broadband Association, 81% of American adults use a smartphone, and there were 374 million internet connections in 2020. The need for additional phone numbers increased with the wide adoption of electronics equipped with data modems and unique phone numbers to access cellular networks.
The North American Numbering Plan (NANP) recognizes different types of overlay plans. These include:
- Distributed overlay
- Multiple-area distributed overlay
- Single concentrated overlay
- Multiple concentrated overlay
- Boundary-extension overlay
In a distributed overlay, the whole area served by an area code gets another area code. Most area code overlays are of this kind. For a multiple-area distributed overlay, two or more existing area codes share a new area code. This occurs if the NANPA or the agency overseeing the assignment of area codes in a state discovers multiple area codes nearing exhaustion but does not anticipate the number of new phone lines in any one area code sufficient to fill up a new area code.
A single concentrated overlay unlocks a new area code for an NPA but only assigns the new code to the parts of this area seeing rapid phone subscriber growth. In this arrangement, the high-growth section has two area codes while the rest of the area only uses the old area code.
Meanwhile, in a multiple concentrated overlay, the entire area served by an area code nearing exhaustion gains multiple new area codes. However, each of these new codes only serves a specific part of the original area. While multiple concentrated overlay is possible, it has not been implemented in the US yet.
Boundary-extension overlay does not lead to the creation of a new area code for a geographic area that needs one. Rather, it involves the expansion of a neighboring area code to accommodate new phone lines assigned in the area under consideration. The extended area code can be the original area code assigned to the neighboring NPA or an overlay code with ample room for new phone numbers.
What Is an Area Code Split?
An area code split involves the division of an existing numbering plan area and the introduction of a new area code. The new area code serves sections of the original NPA, while the old area code keeps serving the other parts not covered by the new code.
A split plan is also a way to expand an NPA and accommodate more phone numbers. Like overlay plans, it is a response to the increasing number of phone users in a geographic area and the rapid adoption of consumer electronic devices requiring dedicated phone lines.
The Disadvantages of an Area Code Split
Split plans have one major disadvantage compared to overlay plans. When an area code is split, phone users covered by the new area code need to update their contact information to reflect the new phone numbers assigned to them. Businesses need to print new stationery, update ads, and make new signage. Individual phone users need to send their new phone numbers to friends, family, and acquaintances. The NANPA introduced overlay plans in the mid-1990s to address these issues.
All of these drawbacks are avoided with overlay plans. With overlay codes, existing phone users in an area do not get new phone numbers. Rather, only users getting new phone lines are assigned numbers with the new overlay codes. To keep existing phone users from getting new numbers, overlay plans have quickly replaced split plans as the preferred method of avoiding phone number shortages.
Adopting overlay plans for expanding available phone numbers is not without its own drawback. Chiefly, phone users in places with overlay plans must dial ten digits (including area codes) to place local calls. Before introducing an overlay code, phone users calling within the same NPA only need to dial seven-digit numbers that include prefix codes and line numbers.
What Are Non-Geographic Area Codes?
Non-geographic area codes are special area codes assigned to regional, national, and business services rather than specific numbering plan areas. These include toll-free codes such as 800, 833, 844, 855, 866, 877, and 888. Note that there are more toll-free codes that are not yet active. Examples include 822, 880, 881, 882, 883, 884, 885, 886, 887, and 889.
Other non-geographic area codes include 710 for the US government, 700 for carrier services, and 900 for premium call services. N11 codes are also non-geographic area codes. These offer three-digit dialing for quick access to essential services such as 911.
Who Regulates Area Codes?
Area codes for the US are provided under the North American Numbering Plan (NANP), a program administered by the North American Number Plan Administrator (NANPA). The FCC oversees the function of the Administrator and ensures it provides and regulates area codes in line with the regulations of the NANP. However, the FCC awards the role and position of the NANPA to the private sector.
While the FCC, through the NANPA, regulates area codes introduced in the country, each state has the authority to decide when and how to introduce new area codes within its borders. Usually, this authority lies with the state’s public utility commission or public service commission.
Reverse Phone Lookup and Area Codes
Reverse phone lookup refers to searching for an unknown phone user by their phone number. While a phone user may be able to recognize their area code and those serving nearby counties and cities, out-of-state area codes are more difficult to recognize. To determine the origin of an unknown caller, a reverse phone number search identifies the location by the area code of the phone number used.
Phone number lookup searches can offer more detailed results than callers’ locations. They can also identify unknown callers by name. A free reverse phone lookup can find both the name and address of the subscriber assigned to a phone number. These details are obtained from white page listings of phone numbers and carrier databases. Paid lookup searches turn out additional details by pulling information from more sources. Such premium services are useful for avoiding phone scams and identifying scammers. They are also useful for identifying phone stalkers, spammers, and voice phishers.