The first touch-tone system - which used tones in the voice frequency range
rather than pulses generated by rotary dials - was installed in Baltimore,
Maryland, in 1941. Operators in a central switching office
pushed the buttons; it was much too expensive for general use. However, the
Bell System was intrigued by touch-tone because it increased the speed of
By the early 1960s, low-cost transistors and associated circuit components made the introduction of touch-tone into home telephones possible. Extensive human factors tests determined the position of the buttons to limit errors and increase dialing speed even further. The first commercial touch-tone phones were a big hit in their preview at the 1962 Seattle World's Fair.