Why are there 7 digits in a phone number?

I saw a photo the other day that was dated 1973, and the phone number on a billboard still had a 2-letter prefix then 5 numbers. The billboard was from New York state as I recall. I grew up in Cincinnati, and don't recall ever seeing/hearing/learning any phone numbers that weren't just 7 digits long, all numerals. 1. when did US phone numbers become 7 digits? 2. when did the 2 letter prefix go away?

3. what was the purpose of the 2 letter prefix?

I saw a photo the other day that was dated 1973, and the phone number on a billboard still had a 2-letter prefix then 5 numbers. The billboard was from New York state as I recall. I grew up in Cincinnati, and don't recall ever seeing/hearing/learning any phone numbers that weren't just 7 digits long, all numerals. 1. when did US phone numbers become 7 digits? 2. when did the 2 letter prefix go away?

3. what was the purpose of the 2 letter prefix?

Number dialing came in because the increase in phone subscribers meant it was becoming impossible to come up with enough two-letter combinations that formed the beginning of a word.

Lizzie, you're a font of knowledge, as always!

I struggle with our local numbers now, on landlines, some are a 7 digit dial, some are a 10 digit dial, some are even a 1+, 11 digit dial, and sometimes you just have to experiment and see what works. On my cell phone, everything is a 10 digit dial, but I can't understand most voices on the cell, so I rarely use it.

Phone numbers became standardized at seven figures (letters or numbers) in 1931.

Even though NYC phone "numbers" became standardized at two letters and five numbers in late 1930, I don't think that seven figures became standard in the U.S. until the 1950s.

As we "progress" we are now seeing area codes being overlaid one on top of the other. Growing up in southern Ontario in the 1970s, there was one area code (416) from Niagara Falls to Oshawa around Lake Ontario. Then, 416 was only for Toronto, and the surrounding Golden Horseshoe area became 905. Now, with fax numbers, cell numbers, etc., there are several overlaying area codes because they can't keep up with demand for new numbers.

Add to that mandatory TEN digit dialling (area code first) for local calls. Scary...

My first telephone number; RA-42160, Binghamton, NY, 1954-1959.

-dixon cannon

Lizzie, do you, or anyone else, happen to know what RN (7,6) stood for? That was our exchange in Brooklyn in the 60s and 70s.

That was a "transitional" exchange -- as part of the phase out of the old exchange name system, for a while in the early sixties newly created exchanges might be assigned two letters that didn't stand for an actual name. It was a way of getting around the problem of not having enough meaningful letter combinations to go around while still keeping the familiarity of the two-letter/five-number system.

(My mother was a Bell System operator in those days, until the local exchange went dial in 1965, so she is a fountain of this particular knowledge...)

In actuality, seven figure, dial service "numbers" did not become standardized in the whole country in 1931. I just finished looking at a San Francisco 1945-46 directory, and all the numbers listed are six figures: DO uglas 3352, UN derhill 1702, MA rket 2700, and so on.

-Lee

Just a pedantic moment here... 'standardization' does not equal 'implementation' of said standard. The former in relation to this issue means 'this is what they should be'

The latter means 'wow folks, it may take years and even decades to get to where this standard is true for everyone'

Exactly. This seemed to be standard operating procedure for the Bell System -- to set a standard and then implement it gradually. The 2L-5N standardization was still going on into the early fifties, and came very close to overlapping the start of standardization on all number calling. In both cases, the process took over twenty years to complete.

Agreed

And that's what I was trying to bring out in my first post, that six figure "numbers" did not disappear in 1931, but were gradually phased out by the 1950s.

That was a "transitional" exchange -- as part of the phase out of the old exchange name system, for a while in the early sixties newly created exchanges might be assigned two letters that didn't stand for an actual name. It was a way of getting around the problem of not having enough meaningful letter combinations to go around while still keeping the familiarity of the two-letter/five-number system.

I'm sure there was a lot of variation to all this. Our phone service went to dial in 1960 and we did have the seven digit number with an exchange name. CEdar 4-****. Until into the 1970's though if we were making a local call all we had to dial was 5 digits 4-****. We only needed the extra two digits if it was long distance. At the time there was only one exchange for each community around us so I'm sure this 5 digit dialing was out of convience. The first two digits were the same for everyone so why bother to dial it. This was in the days of mechanical switching so it meant as lot action for the switching mechanisms. My dad used to service the standby generators for the phone company and I went into the local office with him. The building was full of these floor to ceiling switching machines in rows with isles in between clicking and clacking away all day.
Many years earlier my aunt was an operator in a bigger older building full of switch boards. Today those buildings have been sold off and all that equipment is gone.

In the small Michigan town where I attended college in the late 80's, every number in town started with the same two digits so you could make a local call just by dialing the last 5 numbers.

As to the proliferation of area codes, I've always understood it was caused in large part by the increased usage of cell phones. That makes sense to me as a family used to have one phone number, but now, every member of the family might have their own cell phone and their own number.

We recently moved to a hamlet that has exactly ONE three digit prefix. The joke goes like this "one phone prefix, one postal code, three last names - you know you're in a small town when..." !

We had four digit dialing in the town where I grew up, but where I live now it was five digit until about 1993, when the switching system went from mechanical to electronic. Five digit dialing was common in communities with more than one branch in a single exchange -- here, it was LYric 4 and LYric 6.

Another change folks who remember mechanical switching might recall is that the dial tones and busy signals were quite different from what they are today. This is something that they usually get wrong when dubbing telephone sound effects in period movies.

When we moved into a rural area home in 1960 we had a party line and the exchange was LOgan X-XXXX. That changed some time in the mid-60's in eastern Washington...when, I'm doggoned if I can remember.

I saw a photo the other day that was dated 1973, and the phone number on a billboard still had a 2-letter prefix then 5 numbers. The billboard was from New York state as I recall.

3. what was the purpose of the 2 letter prefix?

As Lizzie pointed out, the 2 letter prefix is the exchange name. The two letters ARE the first two numbers. So, a 2-letter prefix, and 5 digit number IS a seven digit number. It was just easier to remember.

KLondike 5-XXXX is a fictional movie 555 number.