Back in high school, late 70’s, I worked in a restaurant that had phones on the tables. Candlestick rotary dial. Up stairs in a stockroom was the switch. Mechanical relays. It was funny going up there an listening to all the relays clicking while people talked to each other across the restaurant.
The only ESS’s I every heard about when I worked for Ma (90’s), were the 4ESS and the 5ESS. Local and long distance respectively.
If your dad was there during the divestiture, I bet he got some nice stock out of it. Those old timers made out pretty good.