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Thomas Farely

Tom has produced privateline.com since 1995. He is now a freelance technology writer who contributes regularly to the site.

His knowledge of telecommunications has served, most notably, the American Heritage Invention and Technology Magazine and The History Channel.
His interview on Alexander Graham Bell will air on the History Channel the end of 2006.

Ken Schmidt

Ken is a licensed attorney who has worked in the tower industry for seven years. He has managed the development of broadcast towers nationwide and developed and built cell towers.

He has been quoted in newspapers and magazines on issues regarding cell towers and has spoke at industry and non-industry conferences on cell tower related issues.

He is recognized as an expert on cell tower leases and due diligence processes for tower acquisitions.

« Bell Lab's History | | London Exchange Names in 1916 »

January 03, 2006

Posted by Tom Farley & Mark van der Hoek at 11:23 PM

Letter Prefixes or EXchange Names


Numbering eras in the United States for the Bell System

* First telephone numbers are just names
* Depending on exchange size, two, three or four digit numbers assigned to subscribers,
* Two letter prefix codes assigned to four digit numbers (Circa 1928 to 1958)
* In larger cities three letter prefix codes assigned to four digit numbers (Post WWII)
* Seven digit, all number dialing begins phase in. (1958)
* Nearly all of North American telephone network converted to all number dialing (1985?)
* Some party lines remain, with single digits like Rodeo Creek Number 8

Was it all a mistake? In January, 1958, Wichita Falls, Texas was the first American city to put in true number calling, that is, seven numerical digits without letters or names. Although it took more than fifteen years to implement throughout the Bell System, ANC, or all number calling, would finally replace the system of letters and numbers begun forty years before at the advent of automatic dial.

AT&T's operating companies started installing dial telephones in the mid to late 1920s. Customers could now dial numbers themselves, instead of having an operator place them as before. Rather than use all digits to indicate a telephone number, AT&T hit upon a hybrid system of letters and numbers. Instead of a number like 351-1017, the Bell System referred to it by a name like ELgin 1-1017, ELliot 1-1017, or ELmwood 1-1017. Something like that. The two letters and a number indicated a customer's switching office or exchange, the last four digits the actual customer's number. But why use letters?

The Bell System thought abbreviations would prevent misdialing, a mnemonic device to help callers unaccustomed to using dial telephones. AT&T's William G. Blauvelt designed a dial with the letters and numbers we use today, one without a Q or Z, one without letters for the digits 1 and 0. The assumption was, therefore, that customers could dial four or five numbers correctly but not six or seven. And that somehow they needed letters as well.

I've never understood, though, why PEnsylvania 6-5000 should be easier to remember or dial than 436-5000. Yet for forty years the most bizarre exchange names flooded the country and the entire telephone system was based on this riot of numbers and letters. It's with some satisfaction I note that AT&T's Joel and Schindler, in A History of Engineering and Science in the Bell System: Switching Technology (1925 -- 1975), in discussing the Texas trial above, state contritely that "later human-factors studies showed there was no need for letters in the dialing sequence." Whoops! They went on to say that people in 1958 were now used to dialing, quite unlike forty years before. Four decades of practice were needed before people could dial another two or three digits? Perhaps. But I doubt it.

The site for all things exchange names: http://ourwebhome.com/TENP/TENproject.html

Officially recommended exchange names: http://ourwebhome.com/TENP/Recommended.html

Without doing a complete research project on this I'd say the Bell System followed the lead of many Independents who were using numbered and lettered dials before AT&T. Bell's regional operating companies may have assumed that letters and numbers were necessary because they were being used, not because they were actually needed. Tradition or sloth set in afterwards and made exchange numbers accepted, unquestioned practice.

The first telephone numbers weren't numbers, they were names. The name of your company or you as an individual. That was too confusing to build a telephone system on since many people in a town might share the same name. Starting in 1879, then, scarcely three years after the telephone was invented, the switch to assigning a customer a number began, with a four digit code being typical. Calls were not dialed by the customer, indeed, there were no dial telephones yet. All calls were connected manually by an operator at a switchboard. But dial telephones would come along.

Let's look at how telephone numbers have been arranged recently, before we look at the numbered and letter scheme of old. Four digit codes allowed 9,999 possible telephone numbers. Plenty for a small town but hardly enough for a big city. What to do? For every block of 9,999 telephone numbers you assign a two or three digit code ahead of it, to designate the telephone switch, just as the four digit code identifies the subscriber. We call the two and then three digit code the prefix or exchange number.

So, if my number was 1017 in one part of town my prefix might be 203, hence 203-1017. Another customer having the same number in another part of town would get another prefix number, say, 481, for 481-1017. The numbers 1 and 0 aren't used for prefixes since so many other things are keyed into those digits. Like dialing 1 before placing a long distance call and dialing 0 before connecting to an operator.





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Letter Prefixes or EXchange Names/ Mobile Telephone Prefixes/ London Exchange Names in 1916

Numbering eras in the United States for the Bell System

* First telephone numbers are just names
* Depending on exchange size, two, three or four digit numbers assigned to subscribers,
* Two letter prefix codes assigned to four digit numbers (Circa 1928 to 1958)
* In larger cities three letter prefix codes assigned to four digit numbers (Post WWII)
* Seven digit, all number dialing begins phase in. (1958)
* Nearly all of North American telephone network converted to all number dialing (1985?)
* Some party lines remain, with single digits like Rodeo Creek Number 8

Was it all a mistake? In January, 1958, Wichita Falls, Texas was the first American city to put in true number calling, that is, seven numerical digits without letters or names. Although it took more than fifteen years to implement throughout the Bell System, ANC, or all number calling, would finally replace the system of letters and numbers begun forty years before at the advent of automatic dial.

AT&T's operating companies started installing dial telephones in the mid to late 1920s. Customers could now dial numbers themselves, instead of having an operator place them as before. Rather than use all digits to indicate a telephone number, AT&T hit upon a hybrid system of letters and numbers. Instead of a number like 351-1017, the Bell System referred to it by a name like ELgin 1-1017, ELliot 1-1017, or ELmwood 1-1017. Something like that. The two letters and a number indicated a customer's switching office or exchange, the last four digits the actual customer's number. But why use letters?

The Bell System thought abbreviations would prevent misdialing, a mnemonic device to help callers unaccustomed to using dial telephones. AT&T's William G. Blauvelt designed a dial with the letters and numbers we use today, one without a Q or Z, one without letters for the digits 1 and 0. The assumption was, therefore, that customers could dial four or five numbers correctly but not six or seven. And that somehow they needed letters as well.

I've never understood, though, why PEnsylvania 6-5000 should be easier to remember or dial than 436-5000. Yet for forty years the most bizarre exchange names flooded the country and the entire telephone system was based on this riot of numbers and letters. It's with some satisfaction I note that AT&T's Joel and Schindler, in A History of Engineering and Science in the Bell System: Switching Technology (1925 -- 1975), in discussing the Texas trial above, state contritely that "later human-factors studies showed there was no need for letters in the dialing sequence." Whoops! They went on to say that people in 1958 were now used to dialing, quite unlike forty years before. Four decades of practice were needed before people could dial another two or three digits? Perhaps. But I doubt it.

The site for all things exchange names: http://ourwebhome.com/TENP/TENproject.html

Officially recommended exchange names: http://ourwebhome.com/TENP/Recommended.html

Without doing a complete research project on this I'd say the Bell System followed the lead of many Independents who were using numbered and lettered dials before AT&T. Bell's regional operating companies may have assumed that letters and numbers were necessary because they were being used, not because they were actually needed. Tradition or sloth set in afterwards and made exchange numbers accepted, unquestioned practice.

The first telephone numbers weren't numbers, they were names. The name of your company or you as an individual. That was too confusing to build a telephone system on since many people in a town might share the same name. Starting in 1879, then, scarcely three years after the telephone was invented, the switch to assigning a customer a number began, with a four digit code being typical. Calls were not dialed by the customer, indeed, there were no dial telephones yet. All calls were connected manually by an operator at a switchboard. But dial telephones would come along.

Let's look at how telephone numbers have been arranged recently, before we look at the numbered and letter scheme of old. Four digit codes allowed 9,999 possible telephone numbers. Plenty for a small town but hardly enough for a big city. What to do? For every block of 9,999 telephone numbers you assign a two or three digit code ahead of it, to designate the telephone switch, just as the four digit code identifies the subscriber. We call the two and then three digit code the prefix or exchange number.

So, if my number was 1017 in one part of town my prefix might be 203, hence 203-1017. Another customer having the same number in another part of town would get another prefix number, say, 481, for 481-1017. The numbers 1 and 0 aren't used for prefixes since so many other things are keyed into those digits. Like dialing 1 before placing a long distance call and dialing 0 before connecting to an operator.

picture of a telephone dial

We then have eight digits which can't be more than three digits long. That means 512 possible office or prefix codes. Which works out to roughly slightly more than five million possible telephone numbers. That's a good system but the one the Bell System settled on for decades was quite limiting. Let's look at that.

As I said before, the Bell System first designated prefixes with letters, not numbers. In the beginning these two letter abbreviations described the area the switch building or central office was located in. Like ELm for an Elm street locale or FRanklin for an exchange on Franklin street. But this sensical method didn't last long as the few central office codes ran out. The problem was there were only so many easily pronounced names, ones where the first two letters of the word wouldn't be confused with other letters. Exchanges were later named for landmarks, famous families, city neighborhoods, and so on. After World War II some two letter prefixes had a number added on to them to extend their usefulness. Something like PLaza1-1017. That gave more prefix possibilities.

People eventually knew exchange names belonged to certain parts of the city and made associations and assumptions based on your telephone number. Did you live in downtown San Francisco? Or were you out by Golden Gate Park? Or near the Marina? Your telephone number gave a clue. All number dialing wiped out all these names and the memories that went them, much angst ensued, and countless editorials mourned their loss. Witness this lament from New York City:

"You could learn about a fella by knowing his exchange. A MOnument fella was up near 100th Street and West End Avenue. You could picture him coming downtown on the IRT, strolling first to 96th and Broadway for the newspapers, passing the Riviera and Riverside movie theaters (both gone). The ATwater girl was an East Side girl, a taxi-hailing girl, on her way to her job at Benton and Bowles. A CIrcle fella was a midtown fella, entering his CIrcle-7 Carnegie-area office with a sandwich from the Stage Deli. And what about a SPring-7 girl, twirling the ends of her long brown hair as she lay on her bed talking to you on te phone? A Greenwich Village girl. A 777 girl is nothing. She is invisible. She is without irony, seldom listens to music."

Jonathan Schwartz, New York Magazine, December 21 -- 28, 1987, as reproduced in Once Upon a Telephone: An Illustrated Social History, (1994) Stern and Gwathmey, New York. Harcourt Brace and Company. p.47

As I mentioned at the top of this page, in 1958 The Bell System began phasing out exchange name dialing or letter prefixes. As Stern and Gwathmey put it, "the WAlnuts, LOcusts, SPruces and MAgnolias were just so much dead wood." As of 1977, nearly two decades later, only 74% of Bell System lines were ANC or all number calling, it would take years more to complete the job, removing a system which was never needed in the first place.

Could you tell me in what year only a 3 digit number was used?

If you want to date something by a telephone number you should contact the history museum nearest the area your interested in. Or look in a local library for old phone books or newspapers with ads that contain telephone numbers. It's really the only way to determine an approximate date, given how every telephone company phased exchange names in and then out.

And please note: I know I sound harsh on exchange names; when I see letters and numbers together my eyes glaze over and I can't focus on what's being communicated. But many people did find them useful in remembering a telephone number and millions still feel sad at their passing; I do not mean to devalue anyone's nostalgia or emotions. Tom Farley

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