During the early years of telephone service, communities that required more than 10,000 telephone numbers, whether dial service was available or not, utilized exchange names to distinguish identical numerics for different customers.

When dial service was introduced (typically during the period of 1910 to 1960) in such multiple exchange communities, typically, customers would dial the first two or three letters of the exchange name, followed by the numeric digits. 1910 was a common year starting on Saturday (see link for calendar). ... 1960 was a leap year starting on Friday (link will take you to calendar). ...

London, England, is most notable for using the first three letters, then the last four digits. New York, USA, was the first American location to use so-called "2-5 numbers", two letters and five numbers. This became the North American standard as long distance service (Direct Distance Dialing came into use through the 1950s. London — containing the City of London — is the capital of the United Kingdom and of England and a major world city. With over seven million inhabitants (Londoners) in Greater London area, it is amongst the most densely populated areas in Western Europe. ... State nickname: Empire State Other U.S. States Capital Albany Largest city New York Governor George Pataki Official languages None (English is de facto) Area 141,205 km² (27th)  - Land 122,409 km²  - Water 18,795 km² (13. ... Direct Distance Dialing was a telephony innovation that enabled subscribers to call long distance numbers (Those outside the local exchange) without having to go though an operator. ... Millennia: 1st millennium - 2nd millennium - 3rd millennium // Events and trends The 1950s in Western society was marked with a sharp rise in the economy for the first time in almost 30 years and return to the 1920s-type consumer society built on credit and boom-times, as well as the...

As demand for phone service grew, the supply of assignable phone numbers began to dwindle, and several North American area codes were split to enable reuse of numbers. As the growth accelerated, the decision was made to switch to All-Number Calling (ANC), since there were several unpronounceable letter combinations that were not being used. This allowed more efficient use of the number supply, and there were only two area code splits between 1962 and 1981.

The standard format for displaying telephone numbers that used exchange names was to capitalize the first few letters if they were dialed, e.g.,

MUrray Hill 5-9975 (one of the Ricardos' numbers on I Love Lucy - note that the H in Hill, although not dialed, is still capitalized) GRamercy 5-1234 (typical North American, in New York or continent-wide after about 1950) BAldwin 6828 (typical urban North American before move to seven-digit numbers) TWIning 3376 (typical London, England, style up to early 1960s) I Love Lucy is a classic and most popular American sitcom from the 1950s, starring comedienne Lucille Ball, her husband Desi Arnaz, Vivian Vance and William Frawley. ...

If they were not dialed, it was more common to only capitalize the first letter of each part of the exchange name, e.g.,

Metcalfe 6000 Fairmont 3335 Metcalfe 200 Fairmont 50

Such numbers could be of non-standard length, simply because they were not dialed, but quoted to an operator that plugged into the appropriate line.

At least one song has been written that uses an exchange name: "PEnnsylvania Six, Five Thousand" (PE 6-5000).

The use of letters in exchange names resulted in placement of letters on the telephone dial. Some areas were not standard (notably Calgary) until later in history. Europe and North America differ in placement of the letter O, and countries with non-English languages differ again.