jjim:
In order for you to reverse the polarity you had to reverse your jumper and my guess is it was actually the temporary disconnect that released the line. I had a situation several months ago that played out on this forum as I fought SBC to prove that they were not sending a DS signal. After almost 3 weeks of joint dispatches and techs looking into the problem, it turned out to be an old SLC96 that had problems and 8 business lines had to be swapped to copper for the problem to go away. That one line being hung do to operator error is probably not a DS issue and if you had a DS issue the lines would hang, especially on the voicemail, anytime an external caller hangs up before the system drops the call. I'm including some verbage from Mike Sandman about DS or CPC (Calling Party Control) depending on what type CO Switch the LEC has and what the Switch manufacturer calls this parameter. I hope that this helps!
FROM MIKE SANDMAN'S WEB SITE:
CPC (Calling Party Control) is a signal sent from most modern electronic COs to indicate that the "Calling Party" has hung up. It's usually called "Open Loop Disconnect" when you're programming telephone equipment.
CPC is normally sent as an open ranging from 250 to 500 milliseconds. Phone equipment at the far end of the call sees this open on the line, and hangs up. Most voice mail and phone systems have a timer setting for CPC. If you set it at 500ms, it usually works fine. If you accidentally set it for 50ms you'll probably get cut-offs, especially during a lightning storm during very brief blips in the loop current. Setting this timer for 50ms means that if the phone equipment sees an open for 1/20th of a second (not very long), it will hang up. Setting it for 500ms means it will hang up if it sees an open of half a second. That's much more reliable.
It's pretty hard to measure CPC timing, but you can at least verify that there is some kind of CPC. Put a volt meter across the line and answer a call. When the calling party hangs up, you should see a blip on your meter. That's the CPC, but most meters can't respond fast enough to show you much of anything. An oscilloscope would show it to you, if you happen to have one around (and know hot to use it).