How is it possible to hear the dial-tone, etc., with the handset unplugged?

[AL_as_needed]

I will say I have an early princess phone that had voltage from the lamp circuit that made for a hum from time to time. There is a slight issue within the hook switch, but it can only be noticed when the phone is on an open line and the lamp is on.

As to the 2500, I think we have been over thinking it, way over thinking it... the answer: Ghosts!