Touch tone phones (DTMF) were first deployed at scale in the US in 1963, but they would have been in development at the Bell System for quite a while before that. Possibly also some limited deployments. This ad from 1956 teases a future without rotary dials.
DTMF also led to the rise of Blue Boxes and Phreaking.
I made a phone kit too later and it wasn’t a real dual tone phone either actually.
When you pressed the 9 button, it just sent 9 pulses at 10 pulses a second.