I have been fascinated by the panel switch, ever since being 'served' by one and noticing its quirks. I finally got to see one in action, BS-ing my way in on a night shift with a friendly tech.
It was really quite ingenious, and very high-tech for ca. 1920!
It can best be described as a 'panel' of open contacts with motor- driven contacts being raised-lowered to select the correct pair and then being 'tripped' to make the connection.
The method to control the thing was almost bass-ackwards from common thinking. The sender in the originating (intra or inter) office told the incoming and final frames when to stop advancing by way of an almost Rube-Goldberg revertive pulse method.
IIRC, tone receivers were simply retrofitted into the register- senders.
I assume this was the way, anyway. As I think back, I really can't recall anybody I knew who was 'served' by a panel office actually having Touch-Tone. I know that (then) 212-436 did not get Touch-Tone until it was cut to ESS in the early 70s. I remember it had a funky nonprecise tone plant until the cut, which would preclude DTMF.
I vaguely remember that 212-355 was panel and had the precise dial tone prior to it being cut, but I can't remember any actual DTMF sets on that office.402-551 and 402-553 were panel into the 70s, and I seem to recall them having precise dial tone, but again, I can't remember any actual subscribers with Touch-Tone service on those offices.
Anybody know for sure if Ma Bell supported Touch-Tone on panel offices? (Carl, you listening in?) ;-)