I found these two intercoms the other day. I haven't been able to find any similar IBM ones by googling.
Judging by the visible circuitry you would open a circuit by lifting the earpiece off the hook and the solenoid would probably operate a buzzer. The other end picking up the earpiece would probably complete the connection, but they look like carbon granule microphones and speakers, so the quality would be poor. Around the middle of the 20th C. I'd say. You'd need a wired connection plus a battery in the circuit somewhere.
Yes, same effect. It's a cousin of the old candlestick telephone, but more 'modern' and directly connected.