A telephone keypad is a keypad that appears on a "Touch Tone" telephone. It was standardised when the dual-tone multi-frequency system in the new push-button telephone was introduced in the 1960s, which gradually replaced the rotary dial. The contemporary keypad is laid out in a 4×3 grid, although the original DTMF system in the new keypad had an additional column for four now-defunct menu selector keys.
Read more about Telephone Keypad: Key Frequency, Letter Mapping, Illumination
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“Language is as real, as tangible, in our lives as streets, pipelines, telephone switchboards, microwaves, radioactivity, cloning laboratories, nuclear power stations.”
—Adrienne Rich (b. 1929)