Explore the fascinating evolution of US phone numbers from their alphanumeric origins to today's 10-digit system, understanding changes and features.
Most of us take for granted the everyday miracle of speaking with someone far away after typing a string of numbers into a phone, but few people look beyond the “Mr. Watson, come here” origin story to how the modern phone number came about.
After Alexander Graham Bell’s first call in 1876, telephone networks gradually proliferated over the ensuing decades as more and more subscribers acquired a home phone. What started out as simple point-to-point connections soon expanded to local and then regional networks, which gradually increased their service areas. As they did so, they adopted individual phone numbering plans, many of which were alphanumeric to assist with memorization, like Murray Hill (MH) 55000.
By the early 1940’s the US telephone service was a disorganized amalgamation of many differing local numbering systems, and it soon became apparent that this could not be allowed to continue, as it made it difficult to interconnect the many local exchanges to facilitate long-distance phone calls.
The ten-digit phone number US residents are familiar with today came about as a result of the North American Numbering Plan (NANP), which was originally established in the 1940’s as part of an effort to standardize the many different local number plans established in the decades following the invention of the telephone. What resulted was a unified, systematic method for assigning phone numbers, which enabled efficient local and long-distance service.
The NANP was officially launched in 1947 as the Nationwide Numbering Plan. It divided most of North America into 86 numbering plan areas (NPAs), each of which was assigned a unique three-digit NPA code, which was eventually referred to as an area code. Area codes were first used exclusively by long distance phone operators who were responsible for connecting calls across local networks, but as technology advanced, this inefficient system was eventually replaced by automated toll-switching systems.
The first customer-dialed direct call using an area code was made on November 10, 1951, and direct distance dialing (DDD) was subsequently introduced across the country. By the early 1960s, DDD had become commonplace in cities and most towns in the United States and Canada.
From those original 86 geographic area codes, the phone network grew with North America’s expanding population. Today, the United States has 317 area codes and Canada has 40.
After the three-digit area code, the next three digits is the prefix, which typically corresponds to a segment of the region encompassed by the area code. The four remaining digits are known as the “line number” which can have 10,000 unique combinations (from 0000 to 9999) for each prefix.
This adds up to hundreds of millions of 10-digit phone numbers, which are divided into 1000-number blocks that the FCC allocates to local exchange carriers, which in turn assign the numbers to service providers, which then assigns them end users.
To help track the millions of phone numbers that are being constantly allocated, reallocated, assigned, and reassigned, the FCC adopted a number Pooling Administration System (PAS) run by Neustar, which is now owned by TransUnion. The PAS publishes a bewildering array of documents, which include guidelines for carriers and service providers that cover every conceivable aspect of phone number administration, including the porting, aging, and assignment of phone numbers.
Pursuant to the Telecommunications Act (1996), all local carriers and service providers are required to offer number portability, which was eventually expanded to include mobile numbers. Number portability enables customers to retain their numbers when changing from one service provider to another. The FCC requires all carriers to allow customers to port their numbers out.
There are two types of number porting, Local Number Portability (LNP) for landlines, and Wireless LNP (WLNP) for mobile numbers. Whether landline or wireless, a number can be ported in three different ways. The one most people are familiar with is inter-carrier porting, which transfers control of a number from one carrier to another. There is also intra-carrier porting, which moves a number from one switch on a carrier network to a different switch on the same network, and number pooling, when blocks of 1000 numbers are assigned to a new carrier.
Just as wine and spirits are aged for a certain period of time before they’re ready for consumption, disconnected phone numbers are also subjected to an aging process, although for far different reasons. Numbers previously assigned to residential customers may be aged for no less than 45 days and no more than 90 days, while numbers previously assigned to business customers may be aged for no less than 45 days and no more than 365 days.
There are multiple reasons for aging numbers. One is to minimize misdirected calls intended for the previous customer after number is reassigned to someone else. Another reason is to allow service providers to offer a disconnecting customer the opportunity to resume service using the same number, and also to allow service providers time to complete their billing cycles for the number.
A growing population coupled with the introduction of new technologies such as cellular and PCS phones, VoIP devices, fax machines, modems, and others requiring access to the phone system eventually drain the pool of available numbers within a given area code. Before this happens, a new area code for the region will be created. Each new area code will make 792 new prefixes available, and as each prefix can have 10,000 potential line numbers, a new area code makes nearly 8 million new numbers available for distribution within that region.
A toll-free telephone number is billed for all arriving calls and is free to call from any landline number. Toll free numbers are designated by a three-digit dialing prefix like the geographic area codes referenced earlier. There seven toll-free prefixes currently in use (800, 833, 844, 855, 866, 877, and 888), and another nine reserved for use in the future.
Toll free numbers are a relatively recent innovation, having been first introduced by AT&T in 1967. Prior to their introduction, toll-free calls were only available by requesting an operator to reverse the charges, also known as calling collect. The operator had to arrange for the called party to accept the charges before manually completing the call. Naturally, this process proved cumbersome for large enterprises with a heavy volume of collect calls, which paved the way for toll-free number development.
Every toll-free telephone number is managed by a RespOrg, which is short for “Responsible Organization.” RespOrgs were established in 1993 as part of an FCC order instituting toll-free number portability. There are now hundreds of RespOrgs ranging in size from large carriers with thousands of numbers to small companies that only control a few.
A “Vanity Number” is a toll-free number that is either easy to remember (888-888-8888) or has digits whose accompanying letters on a telephone keypad spell something meaningful (1-800-TAXICAB).
Vanity numbers first emerged in the 1970s, just a few years after toll-free number services became widespread. FCC regulations mandate that toll-free numbers be allocated on a first come, first served basis, which gives vanity number operators who register as RespOrgs a strong advantage in obtaining the most valuable ones, as they have first access to newly disconnected numbers and to newly introduced toll-free area codes.
Q: How have phone numbers changed over time?
Q: How did phone numbers start?
Q: How did old phone numbers work?
Q: When did phone numbers go from 7 digits to 10?