<P> Even after the assignment of numbers, operators still connected most calls into the early 20th century: "Hello, Central . Get me Underwood - 342 ." Connecting through operators or "Central" was the norm until mechanical direct - dialing of numbers became more common in the 1920s . </P> <P> In rural areas with magneto crank telephones connected to party lines, the local phone number consisted of the line number plus the ringing pattern of the subscriber . To dial a number such as "3R122" meant making a request to the operator the third party line (if making a call off your own local one), followed by turning the telephone's crank once, a short pause, then twice and twice again . Also common was a code of long and short rings, so one party's call might be signaled by two longs and another's by two longs followed by a short . It was not uncommon to have over a dozen ring cadences (and subscribers) on one line . </P> <P> In the most areas of North America, telephone numbers in metropolitan communities consisted of a combination of digits and letters, starting in the 1920s until the 1960s . Letters were translated to dialed digits, a mapping that was displayed directly on the telephone dial . Each of the digits 2 to 9, and sometimes 0, corresponded to a group of typically three letters . The leading two or three letters of a telephone number indicated the exchange name, for example, EDgewood and IVanhoe, and were followed by 5 or 4 digits . The limitations that these system presented in terms of usable names that were easy to distinguish and spell, and the need for a comprehensive numbering plan that enabled direct - distance dialing, led to the introduction of all - number dialing in the 1960s . </P> <P> The use of numbers starting in 555 - (KLondike - 5) to represent fictional numbers in U.S. movies, television, and literature originated in this period . The "555" prefix was reserved for telephone company use and was only consistently used for directory assistance (information), being "555 - 1212" for the local area . An attempt to dial a 555 number from a movie in the real world will always result in an error message when dialed from a phone in the United States . This reduces the likelihood of nuisance calls . Also, QUincy (5 - 5555) was used, because there was no Q available . Phone numbers were traditionally tied down to a single location; because exchanges were "hard - wired", the first three digits of any number were tied to the geographic location of the exchange . </P>

When did they stop using letters in phone numbers
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