Why Did Phone Numbers Use to Start With Letters?

letters in phone number

The standard ten-digit phone number used in America today doesn’t usually leave much to talk about. At best, it is mechanical and uninspiring.

But there was a time when telephone numbers were much more fun. This was when dialing numbers contained words. Yes, you heard it right. And we are not just talking about a few random letters. Your boring ten-digit code used to have recognizable monikers preceding the numerical digits.

Although only a few among us were fortunate enough to have used them firsthand, you can still find references to them in songs, TV shows, and movies from the 50s.

Phone Numbers and Letters: What’s the Connection?

To understand the answer to this question, we first need to look at how the telephone calling system worked in the early days.

When the telephone initially came into use in the US, only a few people had the privilege of owning a phone. So, there was no real need for a numbering system and each user was identified by name.

If you wanted to contact someone, all you needed to do was call the switchboard (also called the central office) and ask for the relevant person by name, and the switchboard operator would connect you to them right away.

But this approach had limitations. As more people subscribed to phones, it became increasingly difficult for an operator to accommodate connection requests quickly. Things also got complicated when more than one subscriber had the same name.

And so began the introduction of a numbering system.

But the ten-digit dialing numbers you are familiar with didn’t appear overnight. The phone number as we know it has gone through a few phases of change over the decades before finally settling with a ten-digit format.

The most notable of these phases is the introduction of letters or recognizable words representing telephone exchanges. 

Why Name a Telephone Exchange?

old telephone numbers with letters

As demand for phones grew, handling large volumes of requests became challenging for the switchboard operator. And the process of identifying individuals by their names affected the speed of connecting phone users.

So, in the 1920s, direct dial service using a telephone number began. A telephone exchange routed the calls, and callers no longer had to speak to an operator. It was a critical step for enabling nationwide dialing while catering to the rapidly increasing number of phone users.

The assigned telephone numbers consisted of letters and digits.

Letters appeared at the beginning of a number, representing the local telephone exchange. This was important since each area had its own central office. Larger cities and those with a high population density had several.

It was a time when Americans were making more and more long-distance calls. The central office name in a number made it possible to identify local calls and also signaled where a call should be routed.

At various points prior to the 1950s, phone numbers had two or three letters and four or five digits. Two letters with three digits (2L-3N) and three letters with four digits (3L-4N) were some of the popular formats at the time.

But what did these telephone numbers containing letter prefixes actually look like?

Prefixes were specific words that helped identify telephone exchanges. Sometimes, exchanges were named after cities, while parks and other location monikers were not unheard of either.

MArket 7032, for example, is a 2L-4N exchange number, where Market is the central office name. The first two letters to be dialed (in this case, MA) are always in capital and emboldened.

And each letter represents a digit on the rotary dial. Digits “two” to “nine” were assigned for every three letters in the alphabet, from “A” to “Y”. “Zero” stood for “Z” while “one” was unassigned.

Based on this, MArket 7032 was dialed as 62-7032.

The Introduction of the 2L-5N System

After World War II, the 2L-5N telephone system became widely adopted. This included two letter codes used as exchange prefixes, followed by five numbers.

A good example number for 2L-5N is MUrray Hill 5-9975, which anyone who has watched the 1950s show I Love Lucy would recognize.

The first two prefixes, MU, indicated the East Side of Manhattan’s telephone exchange name. The first letter, “M”, stood for “6”, and “U” represented “8” on the rotary phone. This translated the dialing phone number to 685-9975, where the first two digits were derived from the letters “M” and “U”.

Similarly, BUtterfield 5-1212 was dialed as 285-1212.

But you have to admit, MUrray Hill 5-9975 and BUtterfield 5-1212 are far more memorable names than 685-9975 or 285-1212. These old telephone exchange names also sound much more fun.

The Transition to the Modern-Day Phone Number

phone numbers with letters

The telephone exchange name system soon faced a challenge — it didn’t seem capable of accommodating the unanticipated surge of phone users and the expected demand in the future.

The North American Numbering Plan (NANP) designed by the American Telephone and Telegraph Company (AT&T) for the Bell System needed an update.

And so began the implementation of all-number calling or ANC. This eliminated the letters and words that represented exchange names, transitioning the seven-digit dialing number to a format that contained ten numerical digits.

The new format started with a three-digit area code, followed by three digits to identify the central office and four digits that are unique to the phone number.

All-number calling was met with opposition from phone users who had grown fond of the prefix names at the time. The Anti Digit Dialing League and similar groups even launched campaigns against the “dehumanization” of the phone number.

However, this new ten-digit format significantly increased the scalability of the numbering plan, creating a sustainable solution to meet future demand.

In the beginning, an area code was assigned to each area in the NANP. But, nowadays, it is common for a city with a large population to have more than one area code with overlays. Los Angeles and New York City are good examples of this.


Phone numbers have gone through a significant evolution before settling with the format we are familiar with today.

In the 1950s, a home phone number with a prefix featuring an exchange moniker was the norm. The inclusion of exchange names made it easier to identify the relevant central office, enabling faster connections, especially for long-distance calls.

It also made phone numbers fun and easy to remember. After all, there was a certain swag to MUrray Hill 5-9975 and BUtterfield 5-1212 that the all-numerical format doesn’t quite have.

However, to address the challenges of scalability, the numerical ten-digit dialing format with area codes was introduced, permanently phasing out the letter prefix.

This all-number format is now adopted for land and cell phone numbers. However, how a phone number is used and treated has come a long way since the days of the exchange name prefix.

We are living in an age when the phone book is a thing of the past and phone numbers have more to do with data usage than making calls. They have also become unique identifiers that tie up personal digital data, giving way to facilities such as reverse number searches.

The advantages of the ten-digit number are certainly irrefutable. But you just can’t deny the charm of the 50s’ exchange name prefix.


Why did the old telephone exchange require a name?

The growing usage of phones resulted in setting up more and more telephone exchanges across the US.

Certain areas had more than one central office to accommodate the demand. So, having a way to identify each telephone exchange became important to enable a faster connection, especially between different localities. This led to the introduction of a naming technique designed to help determine the exact switching system of a number.

When did the US stop using letters in phone numbers?

Phone numbers that didn’t contain letters were first implemented in 1958. By the mid-1960s, many areas in the US had switched to all-number calling. However, the complete transition to this new number format took longer and was only achieved in the 1980s.

When did the ten-digit telephone number come into use?

A direct call using a ten-digit number was first made in 1951. However, it was not necessary to dial the first three digits (i.e., the area code) for local calls. This means calls within the same numbering plan area or exchange area only required a seven-digit number that contained the central office code and the four-digit line number.

But this changed on October 24, 2021, when using the ten-digit format, even when calling local numbers, became mandatory.

Why were area codes introduced?

By giving way to a ten-digit number format, area codes made it possible to issue more unique phone numbers, addressing a significant limitation in the earlier formats that contained fewer digits.

Issuing new area codes as overlays is also easier if a specific area exceeds the issuable numbers due to high demand. This makes area codes a substantially flexible and scalable long-term solution for future supply needs.

How many area codes are there in the US?

At the beginning of 2024, there were 317 geographic and 18 non-geographic codes in the US, totaling 335 area codes. This number continues to grow as new codes are added to the system.

For instance, several new ones are already planned for and, in some places, implemented in 2024. These include 738 for Los Angeles, 924 for Minnesota, and 821 for Upstate South Carolina.

Eugene Kirdzei
Eugene Kirdzei

Chief Technical Officer at Nuwber
With nearly two decades of experience in the IT industry, Eugene possesses comprehensive knowledge across his professional field, including in data management, data protection, and information search. Through his writing, he aims to provide valuable insights and practical advice on how to safely explore the online environment and leverage digital tools to enhance people’s lives.