When did the push-button telephone go into service?

[bol-anon nga cebuano]

On November 18, 1963, push-button phones became commercially available in two Pennsylvania cities as an alternative to rotary-dial phones; it was offered for an extra fee. The newfangled phones had been introduced at the Seattle World's Fair the year before. The most popular style of telephones was the Model 500, created by industrial designer Henry Dreyfuss. Following the basic design of the rotary-dial phones, it made an easy transition to the touch-tone system, with the four rows of numbers taking the place of the dial. Since each number had a different tone back then, you could actually play a tune by dialing a phone number. There were even song books published, with the numbers taking the place of notes on a staff.

[comran]

When did they start on the initial designs? When was the final prototype launched?