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What do the numbers in your phone number stand for? Getty Images/Image SourceYou might not think about it, but have you ever wondered what the numbers in a phone number actually signify? In simple terms, they serve as an address, much like a computer's IP address. The number of digits in a phone number varies by country, ranging from just five or six digits in rural areas to 10 or more in larger cities.
In the United States, phone numbers are fixed-length, consisting of 10 digits in total. This system was introduced in the late 1940s when AT&T created the North American Numbering Plan (NANP) to streamline long-distance dialing. The plan was implemented in 1951. NANP numbers have 10 digits: a three-digit area code followed by a seven-digit local number. The standard format is typically shown as NXX-NXX-XXXX.
- Area code: Managed by the Federal Communications Commission (FCC), area codes assign specific geographic regions like cities or parts of states. There are 86 original area codes, established in 1947.
- Prefix: The prefix once referred to the specific switch a phone line was connected to. Each switch at a carrier's central office had its own three-digit code. With the advent of computerized switches, systems now enable local number portability (LNP). Today, the prefix indicates a customer's location, down to the city.
- Line number: This is the unique identifier for the phone line being called. These numbers are assigned to the line itself, not the phone, which is why it’s easy to switch phones or add more to the same line.
Think of the three parts of a phone number like a street address: the area code is the city, the prefix is the street, and the line number is the house.
When calling abroad, you need to dial 011, which is 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. Additionally, some countries require city codes, which are dialed after the country code but before the local number.
Understanding Area Codes
The U.S. has a large number of area codes, as shown in this map of just the Northeast. Scott Rothstein/ShutterstockCurrently, the U.S. has nearly 350 geographic area codes, along with 25 non-geographic area codes and additional ones still awaiting activation. California is home to 36 area codes, the highest number of any state.
When the phone system was introduced in the 1940s, blocks of 10,000 phone numbers were assigned to a single carrier within one region. This was generally enough for both small and large towns. However, in the 1990s, with the arrival of cell phones, the demand for more phone numbers surged. The growth of the internet and voice over IP (VOIP) technology, as well as cable companies, further amplified the need for new numbers and area codes.
For many years, new area codes were created by splitting an existing area code into smaller regions. The more populated areas retained the original area code, while less populated areas were assigned the new code.
Instead of splitting the old area codes, overlay area codes now add more phone numbers within the same geographical area as the original. The introduction of overlay area codes required people to start dialing 10 digits, even for local calls.
In Georgia, for example, 404 was the original area code established in 1951. Over the years, the Atlanta area has added multiple area codes to keep up with the growing number of phone numbers, including 770, 678, and 470. In March 2022, the Georgia Public Service Commission approved the newest overlay area code for metro Atlanta, 943. New phone numbers with the 943 area code won’t be assigned until all available numbers from the existing codes are used up.
Nowadays, all new area codes are introduced as overlay codes. There are no longer any cities in the U.S. where you can dial just seven digits to complete a call. This changed on May 14, 2022, when the FCC designated 988 as the three-digit number for the National Suicide Prevention Lifeline (similar to how dialing 911 connects to emergency services). As a result, 82 area codes across 35 states had to transition to 10-digit dialing for all calls.
Starting on July 16, 2022, dialing 988 will route your call to the National Suicide Prevention Lifeline for support and assistance.
