when did push button phones come out in the uk
Push-button telephone In the UK, a brief excursion from standards, GPO telecoms introduced in 1968 their first push-button telephone, the GPO 726 (Ericsson N2000 series [22]), that used neither pulse dialing nor DTMF tones. It used a DC signalling system comprising a number of rectifier diodes[23] arranged in different polarity configuration according to the button pressed. The 726 also requires a ground wire as well as the usual A and B wires. The irony was that with the few installations, the dial signal still had to be converted to pulses in the host PABX. It is now a rare device.