While cleaning out a closet, I came across an old Western Electric 302 telephone from 1945. I’d acquired it in a batch of phones a few years ago, but the rest of the phones were accidentally thrown away.
Stripped down a modular cord, wired it up to the red and green wires coming out of the phone, and it works! Doesn’t ring yet, because I still need to make a couple of modifications. This phone has red/green/white wires, with white being ring voltage, while modern phones just run off red and green (tip and ring). You can dial, answer calls, etc, just fine.