The Bell System tried out Touch Tone service in the early 1960s and made it a formal commercial service beginning in 1963. Slowly nationwide exchanges were modified to support it.
Would anyone know how Independent (non-Bell System) phone companies handled the conversion to Touch Tone? For instance, when did GTE/AE, the biggest Independent, develop TT telephone sets and switchgear and offer it to its customers? How about other large independents? (I remember GTE/AE pay phones that had smaller rectangular buttons instead of the square ones of Bell phones).
Many Independents had small Step by Step exchanges which were not as efficient to convert to TT since basically a frequency converter translated the tones into pulses. The Bell System developed several types of converters, including an inexpensive one (see Bell System History).