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A Staff Report by the Straight Dope Science Advisory Board
1-May-2007
Dear Straight Dope:
When they give a phone number in old movies
and TV shows, they are read as "Plaza 56892" or "Circle 8745." What did this
mean, and how/why did they change from that format to what we use now? —Mike N.,
North Hollywood, CA
SDSTAFF Bricker responds:
Thanks, Mike, for making me feel old.
In the fledgling years of telephone service, the format for telephone numbers
was the name of the telephone exchange followed by (usually) a four-digit
number. A telephone exchange was a central switching office manned by legions of
operators in front of switchboards wired directly to all the telephones in the
neighborhood. In those early days, telephones were almost completely manual: you
made a phone call by simply lifting your phone instrument. The phone operator in
that central office would see the light and buzzer corresponding to your line,
plug in with her headphones (the overwhelming majority of operators being
female, you’ll forgive the use of the gender-specific pronoun here), and ask you
pleasantly, “Number, please?” You would give her the number you wished to call,
and if that number was served by the same central office, she would simply plug
your line into the destination line on the switchboard. If you were calling
across town, to a number served by another central office, she'd plug into a
“trunk line,” a connection to that other office, and ask the operator there to
complete your call by connecting you to the destination phone.
Each exchange was given a name – often the name of the neighborhood or prominent
local feature. This was considered easy for people to remember – your phone
number was your neighborhood exchange, say, “Jefferson” or “Plaza,” with your
individual number appended.
As automatic switching equipment began to replace local exchange operators,
telephones got dials – mechanical wheels with numbered holes that could be spun
to a stop point and then released. The dial would send clicks down the wire that
the automatic switching equipment would recognize as a number. With the practice
of named exchanges firmly entrenched, each number on the phone dial, with the
exception of ‘0’ and ‘1,’ was assigned letters: ‘2’ was ‘ABC,’ ‘3’ was ‘DEF’ and
so on. ‘Q’ and ‘Z’ were little used and so left out, leaving three letters per
each digit 2 through 9. Exchanges were numbered using this code. For example,
the Jefferson exchange was given 533 (J=5, E=3, F=3). To call Jefferson 6385,
you dialed 533 for JEFferson followed by 6385. Exchanges could be configured
with multiple offices if they served more than 10,000 numbers but that required
an additional digit, giving rise to the two-letter, five number format familiar
to those who were kids in the 1950s: JEfferson 3-6385 was different from
JEfferson 2-6385.
This system lasted into the sixties, with businesses using the exchange name as
part of their advertising. But the number of possible exchanges was limited –
try creating a pronounceable name from 5-7 (JKL/PRS) or 9-5 (WXY/JKL), for
example. In 1961, the New York telephone company started using “selected letter”
exchange numbering, in which the letters didn't stand for a word. By the
mid-1960s, the use of letters in new phone numbers had been abandoned in favor
of seven digits, although holders of existing phone numbers continued to use the
exchange names from habit. You, or more likely your grandparents, may recall the
Glenn Miller hit “Pennsylvania 6-5000.” This was the number of the Hotel
Pennsylvania in New York City, 7th Avenue at 33rd Street, whose number today is
still 736-5000.
To test switch functions, the test number 555-5555 was used – exactly halfway
down the switch panel and halfway in each bank. The 555 (“KLondike”) exchange
was never assigned to ordinary phone subscribers; dialing it connected you to
the directory assistance operator, and it became a handy device for fictional
phone numbers, as Cecil explains
here.
Now get off my lawn, get a haircut, and stop listening to that rock and roll!
—SDSTAFF Bricker
Straight Dope Science Advisory Board
Staff Reports are researched and written by members of the Straight Dope Science Advisory Board, Cecil's online auxiliary. Although the SDSAB does its best, these articles are edited by Ed Zotti, not Cecil, so accuracywise you'd better keep your fingers crossed.
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