Chris, I'm wondering if the solenoid releasing the line keys was designed to prevent you from accidentally disconnecting someone.

Situation:

A puts caller on line 1 on hold and does something else in the mean time.

B has line 1 depressed from last call, but hung up. B picks up phone without looking at lamp status. Expects dial tone, doesn't get it and depresses line 2. Caller on line 1 is disconnected.

With all buttons restored every time you hang up you must physically select a line and force you to look at line status.

Sam

"Where are we going and why are we in this hand basket?"