What Do the Digits in Phone Numbers Mean?

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You probably never think about it, but what do the numbers in a phone number actually mean? Essentially, these numbers function as an address, similar to a computer’s IP address. The number of digits in a phone number varies by country, ranging from five or six digits in small towns to 10 or more in large cities.

In the United States, phone numbers have a fixed length of 10 digits. This system dates back to the late 1940s when AT&T developed the North American Numbering Plan (NANP) to simplify long-distance dialing. The plan went into effect in 1951, establishing the current 10-digit format: a three-digit area code followed by a seven-digit local number, represented as NXX-NXX-XXXX.

Components of a Phone Number:

  • Area Code: Regulated by the Federal Communications Commission (FCC), area codes designate specific geographic regions, such as a city or part of a state. There were originally 86 area codes established in 1947.
  • Prefix: Initially, the prefix referred to the specific switch a phone line connected to, each with a unique three-digit number. With the advent of computerized switches, systems now allow local number portability (LNP). Today, the prefix indicates a customer’s location, down to the city level.
  • Line Number: This number identifies the specific phone line being called. These numbers are tied to the line, not the phone itself, which is why you can change phones or add multiple phones to the same line.

Think of these three parts like a street address, where the area code is the city, the prefix is the street, and the line number is the house.

International Calls

When calling another country, you must first dial 011, the international access code, followed by the country code. Calls from the U.S. to Canada and most Caribbean nations can be made without dialing 011 first. Some countries also have city codes, which are dialed after the country code but before the local number.

Growth and Changes in Area Codes

Today, the U.S. has nearly 350 geographic area codes in use, plus 25 non-geographic area codes and others that are not yet in service. California uses the most area codes of any state, currently at 36.

Initially, blocks of 10,000 phone numbers were assigned to one phone carrier in a region, sufficient for both small and large towns. However, the 1990s saw a surge in demand for new phone numbers due to the rise of cell phones, the internet, VOIP, and cable companies.

For decades, new area codes were added by splitting existing ones into more regions. The most populated areas retained the existing area code, while less populated areas received new ones.

Instead of splitting area codes, overlay area codes now increase the number of available phone numbers within the same geographic region. This change necessitated the use of 10-digit dialing, even for local calls.

For instance, Georgia’s original 404 area code, implemented in 1951, has seen numerous additions, including 770, 678, and 470, to accommodate new phone numbers. In March 2022, the Georgia Public Service Commission approved the 943 overlay area code for metro Atlanta, which will be assigned once existing codes run out.

Today, all new area codes are added as overlays. There are no U.S. cities where you can dial a seven-digit number to complete a call. This practice ended on May 14, 2022, after the FCC designated 988 as the National Suicide Prevention Lifeline number. Consequently, 82 area codes in 35 states that used 988 in their local exchanges transitioned to 10-digit dialing for all calls.

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