© Mark Ollig
Shortly after World War II, AT&T’s Long Line Department switchboard toll operators began using pushbutton keys.
These keys generated MF (multi-frequency) tone signals to set up and route calls for telephone subscribers.
MF signaling reduces the time for operator-assisted calls to be processed through switching equipment within the long-distance network.
For decades, when a telephone subscriber called a number, they used a round rotary dial finger wheel attached to the telephone.
Calling a number could take up to 30 seconds as the first digit dialed needed to complete its recoil-spring rotation cycle before dialing the next digit.
While dialing a number, the caller commonly hears sounds described as “clicks” (electrical phone line interruptions during pulse dialing) in the receiver of the telephone’s handset.
During the late 1940s, engineers from Bell Telephone Laboratories worked on a subscriber telephone using pushbuttons rather than a rotary dial to transmit digits.
One experiment involved modifying a 1947 Western Electric model 302 desk phone.
Western Electric was the equipment manufacturer of AT&T's Bell Telephone System.
The model 302 phone’s rotary dial was replaced with a ten-button horizontal arrangement of pushbuttons, with digits one, two, three, four, and five on the top row and six, seven, eight, nine, and zero below it.
Instead of generating MF tones, which are exclusively used by equipment within the long-distance network, the phone produced metallic tones from 10 rectangular three-inch metal reeds attached to the base inside the telephone.
When a subscriber pressed a pushbutton digit, a metal reed was plucked like a stringed bass instrument, generating a unique audible tone vibration.
The metallic tones of the called number would be transmitted over the phone line to the telephone company’s switching equipment, where they would be processed. The calling party would then be routed to the called party’s telephone.
In 1948, 35 metal-reed pushbutton phones were installed and tested from the homes of Bell Telephone Company employees in Pennsylvania.
The test results were unsuccessful.
Bell Telephone engineers discovered the slightest bit of static or noise on the line caused audio level discrepancies in the metallic tones received by the telephone office switching equipment.
Missing, garbled, or incomplete metallic tone transmissions resulted in many failed calls.
Also, the metal reeds would not operate correctly if the telephone were slightly bumped or jarred while pressing a button.
You can hear the metallic tones from a modified 1947 Western Electric 302 telephone calling 978-555-1212 at https://bit.ly/3fBspNR.
Nov. 1, 1960, AT&T began a two-year field trial with telephones in Findlay, OH, equipped with a new pushbutton signaling method called dual-tone multi-frequency (DTMF).
For example, when the digit “four” button is pressed, a combination of the high-frequency 1,209 Hz and the low-frequency 770 Hz tones are audibly generated and processed by the telephone company’s switching equipment.
Due to the initial success of the test trial in Findlay, Bell Telephone Company hurried a large-scale test assessment of telephones equipped with DTMF pushbuttons.
On April 1, 1962, hundreds of telephone subscribers in Greensburg, PA, volunteered to participate in a real-world testing of touch-tone telephones manufactured by Western Electric.
Bell Telephone Company connected the Greensburg touch-tone telephones to DTMF receiver-converter equipment at their central office. Modifications to originating dial-register circuitry in the Western Electric Crossbar No. 5 telephone switching system allowed calls placed by touch-tone telephones to be processed.
Success. Thousands of touch-tone telephone test calls were processed error-free by the telephone switching system.
“Greensburg Homes Test ‘Touch Tone,’” was April 5, 1962, headline of the story in The Pittsburgh Press newspaper.
“Telephone testers like the musical notes that replace dial clicks,” the story began.
“Instead of twirling the familiar dial, one simply touches seven buttons [today we use ten] in rapid succession and waits for the familiar ring at the other end of the line,” the article added.
The story went on to say using pushbuttons takes “two to three seconds to ‘dial’ this way, compared with 25 to 30 seconds on a dial phone.”
In addition, the telephone testers were “delighted by a succession of soft, varied musical notes” instead of the repetitious clicking while making a call.
The article mentioned some testers discovered songs, such as “Mary Had a Little Lamb,” could be played by pressing touch-tone buttons in the correct order.
By the end of 1963, Western Electric had manufactured 20,000 touch-tone telephones with ten buttons labeled zero through nine.
On Nov. 18, 1963, The Bell Telephone System installed the first commercial touch-tone telephones in Pennsylvania homes and businesses.
On Sept. 6, 1964, Northwestern Bell Telephone Company installed the first Minnesota touch-tone telephones in the Minneapolis Bryn-Mawr (Big Hill) and Kenwood neighborhoods.
In 1968, Western Electric added the asterisk/star (*) and hash/pound/number symbol (#) buttons on the touch-tone telephone for accessing “future telephone-based computer systems.”
Today, these buttons are used with telephone banking, security authentication, and features such as speed calling, call forwarding, last call return, and others.
In 1960, AT&T obtained a trademark for the word “touch-tone,” referring to its dual-tone multi-frequency signaling method used with pushbutton telephones.
Using touch-tone is the worldwide standard, whether activated by pushing a button, pressing a flat screen, or using a voice command.
We have come a long way from “twirling the familiar dial.”
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| Modified 1947 Western Electric model 302 desk phone. |
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| Modified 1947 Western Electric model 302 desk phone. |
