Once Mike joined conspiracy, switching was no problem. I had in workshop most of what I needed; bought some items and liberated others. Drilled a tiny hole from workshop to phone cupboard and another to Wyoh’s room—virgin rock a meter thick but a laser drill collimated to a thin pencil cuts rapidly. I unshipped listed phone, made a wireless coupling to line in its recess and concealed it. All else needed were binaural receptors and a speaker in Wyoh’s room, concealed, and same in mine, and a circuit to raise frequency above audio to have silence on Davis phone line, and its converse to restore audio incoming.