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Why We Use 7 Digits and Other Fun Phone Facts

While few phone numbers flow as well as Tommy Tutone’s “867-5309/Jenny” song, there is a science behind the way we structure our telephone digits. So read on below to learn why we make use of both memory and 7 digits to make a call, how area codes became a (necessary) thing, and what you used to call before 9-1-1.

How Phone Numbers Were Invented

Alexander Graham Bell made the first telephone call in 1876 to the only other device in the world that could receive it. Soon after, he knew the system he’d invented to vocally connect the country would spread like wildfire. And as more and more folks bought a telephone and wanted to talk from afar, he had to develop a better way to get connected than by asking for someone by name.

Back in the early days of phone service, you’d have to pick up the receiver, ask the station operator to patch you through to another person, and then wait for your line to be literally plugged into another person’s line. Fearing that if a town’s phone operators fell ill, replacement ones would struggle to run the system, it was soon converted to using 4-digit number sequences instead of names.

The Magical Number 7 (Plus or Minus 2)

As the numeric telephone system grew evermore popular and advanced, the initial 4-digit number sequence was quickly being exhausted. The telephone engineers then devised a 7-digit system to expand their pool of possible number combinations. The first 3 digits would correspond to a certain home telephone service provider, and the last 4 digits would remain as the personal calling code. This made phone numbers both distinguishable enough from one another and easier to remember, and there’s science behind why.

Out short-term memory is a finite resource. Countless psychological experiments have shown that, on average, the unaided observer is severely limited in terms of the amount of information he or she can receive, process, and remember. In fact, the longest sequence a normal person can recall on the fly contains about seven items. This limit, which psychologist George Miller dubbed as the “magical number seven” when he discovered it in 1956, explains some of the bounds on our capacity for processing information. And, essentially, the brain’s short-term memory can hold 7 chunks of information – plus or minus 2 for the sake of variation in human processing speed and capacity. Later on, psychologists also learned that – by the use of various techniques like repeated rehearsal, chunking bits of information, and using mnemonic devices – humans can slightly expand this informational bottleneck.

And so, the speech pattern of using the 3-4 digit sequences, combined with the repetition of the provider codes and the rhyming patterns of certain number sequences, made for more memorable phone numbers.

The Birth of Area Codes, or Why We Needed More Numbers

Eventually, 7 digits also weren’t enough to handle the demand of callers hungry for the technology that telephone was dishing out. And so, telephone engineers then added 3 more digits to the front of the series of numbers, an area code – the next evolution of the original North American Numbering Plan.

The prefix area code system and the 3-3-4 dialing scheme developed by AT&T became established as the dialing standard in 1951. Back then, codes were dished out based on population, and the areas with the largest populations (ranging from a whole state to a single city) received codes that were the quickest to dial on a rotary phone. States that required more than about 500 central phone operator offices – a technical limitation of the number plan – were split into multiple areas. Each successive area received its own code – with the middle digit being 1 – while area codes that covered an entire state kept the digit 0 in the middle.

The effect was that the most densely-populated cities had area codes that produced the shortest pulse sequences. For example, while the first area code installed was 201 for New Jersey and the District of Columbia received the second code of 202, New York City claimed area code 212, having only five pulses, the shortest of all area codes. Also, calls crossing into different area codes required special toll-switching systems, and so the Bell System organized the numbering plan to minimize the cost of providing automatic dialing to large population centers.

With the rapid growth of telephony in the late 20th century, large metropolitan areas also saw the introduction of overlay codes in the mid and late 1990s. Overlay codes allowed for two or more area codes to exist within the same geographical vicinity. It also saved the company from having to do a restructuring of the initial area codes and to make many customers change their phone numbers. As a result, phone providers instituted mandatory ten-digit dialing rules to prevent any confusion, requiring that the area code be dialed for all calls, though the country code (“1” for the United States) remains optional for local calls in some of these areas.

Before 9-1-1 Was THE Emergency Number

Of course, there are still some phone numbers we keep aside that don’t abide by the 7-digit rule. And while 9-1-1 was eventually adopted as the standard emergency number in the United States and Canada, this was not official until the late 1960s. Prior to the one-number emergency system, you’d have to call the operator to summon the correct emergency service. Or, in some states, you’d dial “3-4-7-3” – which spells “FIRE” – to reach your local fire department. (You can imagine how effective that was while counting the number of buildings burning down.) And, even though this number was first known as “nine-eleven,” the phone companies changed the stylization of it to “nine-one-one” to avoid confusion with people wasting precious time looking for the elusive “11” button that never existed.

So, the next time you pick up your phone to connect with your friends and family both near and far, remember how much this technology has progressed. You can feel glad knowing that these simple numbers can carry your voice such great lengths.

(P.S. – Just don’t dial the number (212) 664-7665. It’s a fake number that Universal Studios owns and uses in a number of popular movies, and you’ll hear nothing but endless rings and rings and rings.)

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