History of US Phone Number: From 1910 to 2016.

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USA Phone Numbering system, from 1910 to 2016.
USA Phone Numbering System, from 1910 to 2016.

It is hard to imagine a world without phones. From none, to a phone in pretty much every home and business. It took a little over a century to achieve.

“Mr. Watson —Come here—I want to see you”.

When the Scottish Inventor spoke his first words, “Mr. Watson —Come here—I want to see you”  into his telephonic device, on March 10th 1876. Even he didn’t have what we all assume to be so common with a phone today. Bell “called” Watson in the adjacent room without dialling a telephone number. In fact having a number was not even in people’s dream. Such was the amazement of the telephonic system enabling one person to speak to another over a series of cables and wires.

“Hello Girl”.

Hello Girls, USA Phone Numbering History
Hello Girls operating switchboards.

Not long after telephone was popular. Cities got their own telephone networks and people subscribed to the telephone service in their city. Every subscriber was assigned a US telephone number and initially phones were connected via an operator or “Hello Girl”.

Operating switchboards.

By 1910, there were an estimated 7 million telephone subscribers in the United States, and growth was rapid. The telephone network grew essentially from the Bell System. The number system was reliant upon the local regional network operators. The initial USA telephone number plan had little, if any structure. The growth of the network with its varied. And unstructured number system was soon seen as a hindrance to growth of the telephone network. It made long distance phone calls difficult.

Bell System Telephone Switchboard.

Bell System Telephone Switchboard
Bell System Telephone Switchboard.

Telecommunications technology and trunk exchanges improved over the next three decades. In the early 1940’s the Bell System started an investigation into a planned national telephone numbering system. The system was to be structured in such a manner, that it would no longer require the use of manned telephone exchanges. Thus adding to the efficiency of the network overall.

National Plan Areas.

National Plan Areas (NPA) were established as regional service areas. Covering the North American continent and were based primarily on the boundary lines of the state or province. A three-digit code was used to identify each individual NPA. Each NPA was established in a manner that met the understood principles of telecommunication. That were considered best to simplify customer use. Also make dialling as easy as possible whilst also reducing costs. The sophisticated network allowed for telephone in its respected area to be identified by a unique 10-digit US telephone number.

10 Digit Phone Number.

The 10-digit number was made up as follows:

  • Area Code (First 3 Digits).
  • Subscriber number (7 digits) made up as,
  • Central Office Exchange (3 Digits).
  • Station or Line Number (4 Digits).

The reason for the 4 digits was because the switching systems of the time were made to serve up to 10,000 phones. Letters spelling out the first two letters of the central office name were used.

Early Rotary Dial with Letters.

Early Rotary Dial with Letters
Early Rotary Dial with Letters

Based in the system developed by W G Blauvelt. Where letters were grouped on the dialling digits 2 through 9. This lettering and numbering system is still used today. It has perhaps been one of the single most important telecommunication developments in history.  The system initially designed to assist the Bell System manage the numbering systems of large metropolitan areas, helping early telephone users identify where they were calling.  The North American telephone exchange network eventually moved towards a 2-Letter 5-digit system nationally.

The New Network Design.

By 1947 the telephone network had grown. The new network design was complete with 152 area codes and 540 central offices throughout the North American continent. At first only 86 area codes were assigned with New Jersey receiving the first USA telephone number, area code 201. New Jersey was shortly followed by area code 202 for the District of Columbia.

Changes to the numbering system.

Within a year certain inadequacies in some metropolitan areas surfaced. Changes to the USA telephone numbering system had to be made. Some codes being split to create a larger number pool in other areas.  An example of this is the area code 317 for Indiana. Which was split to provide for more numbers in the Indiana suburbs of Chicago on area code 219.

Long Distance Telephone Calls

Long-distance operators used the area codes to allow for long-distance telephone calls. Which were made using toll offices. In 1951 what we take for granted today was undertaken. The very first DDD (Direct Distance Dialing) call was made connecting Alameda, CA with Englewood, NJ and this was soon the norm across the entire United States. With the Bell System having been converted making it normal in cities. Most larger built up areas. Long distance calling that we take for granted today accessible to anybody on the phone network.

Lockheed Martin.

From the 1960’s onward, Lockheed Martin IMS that was to become Neustar grew the telephone system. And brought the United States and the outlying territories into the system. All the Caribbean countries, Canada and Bermuda came into the system. Bermuda and the British West indies because of their strong links to Canada as part of the British Commonwealth.

North American Numbering Plan.

What has become called the North American Numbering Plan (NANP). Soon it grew and encompassed many regions and many countries primarily in North America. Not all North American countries participate in NANP with primarily Mexico. The countries in Central America, Cuba, Haiti and the French Caribbean not partaking. There is only one Spanish-speaking country. The Dominican Republic in the plan with Mexican participation stopped in 1991. One of the last counties to join the system was Sint Maarten in 2011.

Countries Participating in NANP.

Rotary dialling, was till common place and the most populous regions were assigned codes. That were easiest and quickest to dial from a rotary phone. The following codes were provided for the following cities:

  • New York City 212
  • Los Angeles 213
  • Chicago 312
  • Detroit 313
  • Philadelphia 215

For areas that covered an entire state the digit 0 was originally planned to be used. As the middle number with 1 in position being reserved for jurisdictions that could be divided into multiple area codes.

Area codes.

Area codes used a simple code structure to build the number using the NYX format as follows:

  • N = Any Number from 2 through 9
  • Y = 0 or 1
  • X = Any number from 1 through 9 if Y = 0
  • X = Any number from 2 through 9 if Y = 1

The code structure

N is restricted to save the digit 0 for operator assistance and leaves 1 to signal long distance calling. To help telephone equipment handle and recognise. The difference in 3 digit area codes that had either 0 or 1 as the second digit. Also the three digit central office prefix that did not use 0 or 1 as the second digit. Early equipment had various limitations that forced the USA telephone numbering system to come about. The code structure was actually very intuitive allowing the equipment to recognition long distance or local calling. For example if the number 202-345-9876 the 202 was picked up as the area code. But if 545-1214 was dialled the 4 would indicate the call would be local, clever indeed.

Telephone Network in 80’s & 90’s

During the 1980s and 1990s the telephone network continued to grow and changes had to be made, to accommodate more US telephone numbers. A new procedure for all long-distance calls within an area had to be prefixed with 1. To make it possible for central offices to be prefixed with 1 or 0 in the middle position. This facilitated the assignment of area codes with a different form N10. San Antonio was assigned 210 on in the Texas area and 410 in the Eastern Maryland area. This meant that someone dialling for Sam Jose to Los Angeles now dialled 1-213-555-1236. Rather than just 213-555-1236 permitting the use of 213 as an exchange prefix in San Jose.

NPA =  Number Plan Area Code

Area Code 212 and Overlays 646 and 917, New York State. With the changes the NANP numbering format can be easily summarised as NPA-NXX-xxxx defined as above.

The NPA allowed for the first digit to be from 2 through 9 and 0 through 9 for the subsequent two digits.  The code is called an ERC (Easily Recognizable Code). When the last two digits are the same. ERCs are used primarily for special services such as 888 for toll-free USA telephone numbers. The NANP does not assign area codes using 9 as the middle digit.

NXX = Central Office (Exchange) Code

NXX allowed for a number from 2 through 9 for the first digit. A number from 0 through 9 for the last two digits. With the third digit not being 1 if the second is 1 in geographical area codes.

Xxxx = subscriber code

The subscriber code can be any combination of four numbers from 0 through 9. Applying the rules defined the following is attained:

  • 234-235-5678 is valid
  • 234-911-5678 is invalid, because the exchange code cannot be in the form N11. (For non-geographic area codes like +1-800, 9-1-1 remains invalid, but other N-1-1 codes are valid exchange prefixes
  • 281-124-8163 is invalid, because the exchange code must begin with 2-9.
  • 123-234-5678 is invalid, because NPA cannot begin with 0 or 1
  • 281-234-5678 is valid.


The international dialling code in the NANP is +1 for example calling Maryland would be +1-301-555-0100. The long distance code is also 1 within the NANP. Under the structure the three digit area code can contain up to almost 8 million unique US telephone numbers. Providing the base for the almost 8 million numbers is the NXX that may only begin with a number from 2 through 9.Both X and X cannot be 1 to avoid confusion with the special N11 numbers such as 911.

Movie Phone Numbers.

Some 555 numbers as seen in movies and on TV do not exist. From 555-0199 through 555-and is reserved for purely fictional needs. The rest of the 555 numbers are reserved for information numbers. The country calling code for the NANP is +1. In international format. An NANP number should be listed thus: +13015550100 (example using the original area code for Maryland). The trunk prefix code for direct-dialled long-distance in the NANP is also 1.

Telus Payphone in 90s.

There are numbers that are deliberately not used such as 212717-xxxx. Numbers that could cause confusion between an area code and a local exchange number. As both 212 and 718 are New York City area codes.There are two numbers 958-xxx and 959-xxxx that are reserved as test numbers.

To allow for NANP expansion insert a 9 as the middle digit of an area code. And using 0 or 1 as the first digit of an area code or 7-digit local number makes a number invalid.

Increase in Demand.

Because of the increased demand for telephone services. And because of the uptake of fax, modem and more recently mobile communication. The telephone network in Canada and the United States has experienced a continuation of rapid growth. This growth was most notable between 1990 and 2005 as the world found the internet and became more mobile.

Local Telecom Providers.

Furthermore the regulation of local telecommunication services In the United States. That started in the mid-90s, allowed competition between telecommunications companies. and the incumbent local exchange carrier.  The competition often forced the existing sole service provider to lease infrastructure to other local carriers. Where it was then resold to customers. The original design of the USA telephone number plan and the network. That really only allowed for a single sole provider. Meant that new numbers could only be provided in blocks of 10,000.

Limited Phone Numbers.

This unfortunate situation meant that any new local service provider in the market was automatically assigned 10,000 US telephone numbers. Often the service provider has far less than 10,000 customers. This numbers went un-allocated.  This began to create a problem with as more providers entered the market. Who when requesting their numbers and being allocated their 10,000, it was clear that numbers would soon run out.  Using telecom language this meat the network was “in Jeopardy”

Un-allocated Phone Numbers.

As in any growth industry there were of course a number of unsuccessful ventures. And while the number of area codes rapidly grew. This did not correlate with a much larger USA telephone number of telephone subscribers. Many of the numbers in the blocks were un-allocated, due to the methodology being applied. Many telecom ventures were taken over or merged. Which allowed for a continued or improved service. Blocks were transferred but still many remained un-allocated. There was no system or regulatory mechanism in place that could reclaim or reassign under used blocks.

New Are Codes.

Area codes are added to the network essentially through two methods. Firstly through Splits that were implemented. To divide a plan area in to two or more regions of which one retained the existing code. And the newly created regions thus received a new number. Secondly the use of an overlay under which numerous codes can be assigned to the same geographical area. The obviated the need to renumber existing services.

  • Houston, Texas with 4 Area codes- 281, 346, 713, and 832.

Overlay code.

The overlay method has been subtly modified with dedicated overlays and concentrated overlays. With a dedicated overlay a new code is reserved for a particular type of service. Such as a cellular service and with a concentrated overlay part of the area retains a single code. The rest receive an overlay code. The 917 area code (New York City) was the only service-specific overlay. When the NANP was first implemented, later on these service-specific area code assignment were prohibited under the rules of the Federal Communications Commission (FCC).

Technological Advancement.

Technological advancement has seen changes in the US telephone number over the years. It is hard to believe that most of the original N10 codes were once reserved for  AT&T’s Teletypewriter exchange. This just goes to show how far we have moved on. In 1969 these codes were transferred to Western Union and then in 1981 were freed up in 1981. After conversion to Telex II. The last of these codes was assigned to Canada and then liberated in 1992.  Because all other area codes under the original plan were used up.  Codes formerly used as aliases to Mexican number. These “new” area codes were used for telephone area splits in the late 80’s.

More Area Codes.

In 1995 the rapid increase in demand for more area codes. Both splits and overlays, forced a change in the US telephone number. The change allowed the digits 2 through 8 to be used as a middle number. In the new area codes and 9 was reserved as an absolute last resort for future expansion. This change coincided with local exchanges being allowed to use 1 or 0 as a middle digit. The area codes 334 (Alabama) and 360 (Washington), were the first area codes. Not using 1 or 0 as the middle digit in early 1995 followed rapidly Arizona with code 520.

Easily Recognisable Codes.

ERCs (Easily Recognizable Codes) that are codes that end in double digits have been reserved. For special purposes that include toll free numbers such as 800, 888, 866, 855 and 844 as well as personal 500 number. Carrier specific 700 numbers and high toll 900 numbers.

Nevada Phone Codes.

Lucky 777 was denied for Nevada for the very same ERC reason. Instead received 775 when most of the state split from the original 702 code. That continues though to serve the Las Vegas Metro.

7 Digit Codes.

Either through splitting a city into different areas. Or having more than number for an area. Many US and Canadian cities had more than one area code. Manhattan is a good example. Where subscribers have the NPA code 212 with 2 additional codes. 917 that before being struck down in a federal court was in place for cellular communication and then 646. This meant that other other area code had to be dialled. Even when making a “local” call. Today there are many areas that 7 digital dialling is not in use. And 10 or 11 digits have to be dialled instead. The first US City to move to this number is Atlanta. The city was using the 1996 Summer Olympics and the catalyst to bring this about successfully.

Confusion in Dialling Numbers.

Sometimes, there was confusion regarding dialling US telephone numbers. where there is an overlap between area codes and exchange prefixes. Because the 3 digits in both may be identical. Nashua, New Hampshire is a prime example. Where the local exchange code is 603 888. Confusing customers with the toll free 888 numbers. If someone in Nashua accidentally dials 888-555-1212. The user may actually end up calling 603-888-5551. Because they forgot to dial 1 as the prefix. Luckily this is generally not a problem in major metros  with overlapping codes. Because it was mandatory to dial all 10 digits for all local calls.

Decline in the Expansion Rate

Over recent years,there was a decline in the expansion rate of the telephone network. Understanding that the proliferation of area codes was caused by the Telecom Regulation Act. The assignment of large 10,000 number blocks. There are a move to alleviate the number shortage.  In 2001 US telephone number pooling was first tried as a system for allocating groups of numbers in batches of 1,000 opposed to 10,000. This overcame the past technical problems this soon created the problem of number portability that had to be overcome.

Pooling and Porting.

The program of pooling and porting has been somewhat successful. And put in place, by much of the United States. Some cites has implemented rate centre consolidation. This has resulted in a more efficient use of numbers allowing blocks of numbers, to spread across multiple areas.  This process along with the reclaiming of the unused blocks from service providers. Has stemmed the demand for additional area codes with many planed splits. Overlays now postponed completely. Number pooling has reduced the need for additional area code. So that many previously designated area splits and overlays are facing delays, indefinitely.

Modern Telephone Exchange.

We expect that the current US telephone numbering system will be sufficient until 2044.  This is based on the assumption that a maximum of 667 NPAs. Remain available and that there is an average of 4400 central office codes should be available, each year.

There are plans under discussion that allow for an expanded US telephone number plan. One of these plans adds either 1 or 0 to the beginning or the end of the area code or the beginning of the subscriber number. This would require a universal adoption of 11 digit dialling.

150 years on from the very first phone call.

Technology has been the driving change behind the growth and change of the US Telephone numbering system. Who knows where we will be in 2026, 150 years on from the very first phone call?

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