1. The Role of Area Codes in Local and Long-Distance Calling

The first three digits of a phone number—the area code—determine how a call is routed. They are dialed before the seven-digit local phone number.

Initially, the Bell engineers assigned area codes to geographic regions based on population and expected call volumes. They were also chosen for their shortest rotary dialing time.

Learn why the 929-area code is so significant

2. Identifying the Origin or Destination of a Call

Area codes identify a specific geographic region of the country. They facilitate a standardized format that allows for direct-dialed telephone service without the need for operator assistance. Since the introduction of the North American Numbering Plan (NANP) in 1947, area codes have been allocated based on geographic considerations to make it easier for people across the country to communicate with each other.

The implementation of a new area code involves two steps. First, a period of permissive dialing is introduced which allows old and new numbers to be used interchangeably. This period typically lasts for a few months. After the introductory period, mandatory dialing begins and calls must be made using the new 10-digit number.

As the demand for phone numbers grows, geographic areas may become too large for a single area code to handle. In such cases, an area code split or overlay is implemented. A split divides the geographic area into multiple zones while an overlay adds a new number to the existing territory. Both methods are designed to ensure that telephone callers can reach the desired party.

People often feel a connection to their area code. They proudly proclaim their region’s heritage and culture when discussing local events or sports teams. Some even go so far as to design t-shirts and hoodies bearing their area code’s numerals. In a world where mobility is increasing, people move more often than ever before, changing homes, jobs and cities, but one thing most don’t change is their phone numbers.

3. Dialing the Correct Number

The area code is a three-digit number before your local telephone number. It shows from what geographic region your telephone line originates, and it helps speed up connections by eliminating human operators.

Before area codes, phone numbers were a string of letters and digits, usually followed by the name of a city or town. The area code was introduced with AT&T's North American Numbering Plan devised by AT&T in 1947 to organize these numbers and make them easier to dial, especially when using touch-tone phones.

Today, the North American Numbering Plan continues to create new area codes as demand increases for local lines in cities and regions nationwide. When a new area code is added, customers must alert their friends and business associates of the change, which can require them to reprint stationery, business cards, brochures, checks and other printed materials with their updated telephone numbers.

In addition, any automatic dialing equipment, such as PBXs, Internet dial-up systems, fax machines, fire or burglar alarm and gate systems, personal or business phones, speed dialers, home or auto answering services, contact lists, and other devices, may need to be reconfigured to complete calls with 10-digits. These changes can impact your company's productivity and your personal call habits.

4. Managing Limited Resources

When area codes and exchanges were mapped one-to-one with geographic areas, a call to another number within the same exchange was considered local. Today, however, there are many more combinations of seven digits plus the area code than available phone numbers. When the number of possible combinations starts to get low, a process known as an overlay is initiated.

An overlay aims to create a new area code that will manage the number of calls within the existing geographic region by splitting it into several smaller areas. Typically, each new area will have its own name and the prefixes will be moved from the old to the new area code. For example, the 612 area code was split in 2000 to create the new 651 and 763 area codes.

Although most calls are now made over the Internet, long-distance calling remains a vital business. Those revenues pay for networks that connect cell phones, landlines, and even rotary dialers, so it's important that they continue to work properly.

During the breakup of the Bell System in 1984, the concept of the local access and transport area or LATA was created to distinguish between in-region telephone calls (which would be handled by local telephone companies such as the Baby Bells) from out-of-region (or interexchange) calls (which would be handled by long-distance carriers). This is reflected in the use of different area codes to indicate which type of call you are making.

Avoiding Misdialing

As the popularity of telephones grew, area codes were introduced. They were designed to make dialling numbers easier when using rotary phones, with more populated areas getting lower digits and less populated regions getting higher digits. In addition, a popular perception was that a phone number with a local area code made the caller seem more familiar and credible. The popularity of recognizable area codes continues today, with many people choosing to include them in their personal and business numbers to promote brand recognition or to show their roots or loyalty.

The need for area codes continues to grow as new telecommunications services emerge and old ones are eliminated. As a result, area codes occasionally run out of available telephone number prefixes. When this occurs, the North American Numbering Plan Association (NANPA) notifies telecommunications service providers to begin planning for an area code split or overlay.

When an area code is split, it may be divided along geographic boundaries or by a city/area combination. The latter method is preferred because it can avoid the confusion that results from having multiple area codes overlapping in the same region. A key requirement when an area code overlay is implemented is that ten-digit dialing be required for all calls, including local calls, even though the system initially allows seven-digit dialing. This is known as a Permissive Dialing period and typically lasts for several months before mandatory dialing begins.