It must have been around 1980 that I found in a local junk yard some weird looking piece of technology as shown on the right: a Siemens F-selector that had previously been used as a switch in the local analog telephone exchange of Maastricht Central. The F-selector would be able to accept up to 10 electric pulses from a rotary dial to lift a set of switch contacts along a shaft in a vertical manner, and then to accept up to 10 pulses to rotate these switch contacts in a horizontal manner. When moving horizontally, the selector would have the possibility to connect each of its 3 switch contacts to a potential of 100 outlets. I noticed that the selector was marked "Philips" but the frame was marked "Siemens". How come? I found that after world-war-II -as part of post-war damage payments and settlements- Siemens had lost the exclusive rights in the Netherlands to the manufacturing of the patented technology to Philips. Philips were able to restore much of the damaged public switch infrastructure from their own manufacturing plant. Hence the frames would indicate "Siemens" but the switches would be rebuilt by Philips after the war - based on original Siemens design.
Slightly later I had the opportunity to collect a full frame of 20 F-selectors and several 50-step and 18-step selectors frames, so I devised a home PBX that would support up to 25 analog rotary dial phones and one public exchange line. Each of the phones was actually deployed in a room in the immense house I was living in at the time.
The links below provide an overview to the early work.