[Dave Moll]

Yes, the phones (designated "X" and "Y") were indeed wired with their speech circuits in parallel as Peter describes, though the "Y" is connected with "A" and "B" legs reversed to achieve the ringing between the appropriate leg and earth.

In order to make a call, the handset is lifted and a check is made that the other party is not engaged in a call. If the line is free, the "call exchange" button is pressed to obtain a dial tone and the outgoing call then proceeds as normal.

On receiving a call (with ringing on ones appropriate ringer), I seem to recall that one simply had to lift the handset to be connected to the caller. I don't recall having to press "call exchange" in this instance, though it would probably simplify the circuitry if one did.

My question was really to avoid "reinventing the wheel" if someone has already designed a circuit, either by the traditional GPO way using relays or with solid-state electronics, before I try to work out something to make a pair of telephones behave as described above.

And yes, the (no doubt apocryphal) story about the "psychic" dog does crop up from time to time, and is quoted in one of the early issues of the Telecommunications Heritage Journal.