We run an eight or nine phone comdial 8024s system. One of our phones periodically electronically "comes off the hook", with nobody near it. It just grabs a line. I popped it open and mechanically it looks ok. Any ideas?

The Comdial is famous for that problem if the stations are not wired the same through out the system. Lets say that if all your 2nd pairs are the same except for one it could cause that problem with that station and its paired port also.
Hope this helps
dtmf

It is the same phone which will do it no matter where it is plugged in. That wouldn't fit with your scenario, would it?

No it wouldn't. It sounds like its the phone.
More than likely its got flakes from the buttons that is shorting on the mother board.
You might want to get it repaired or get your self a refurb
dtmf

The phone may need a cleaning where the buttons hit the board, in side the pad. Be careful not to clean off the conductive part on the button. I haven't heard of this problem on the 8024 phones, it was always happening on the Executech phones.

Reterminate the wiring at the jack and backboard. Check where you "skinned" the io to make sure you didn't nick a lead. I have found this problem to be symptomatic of a loose connection more than once.