Sounds to me you would be better off at McDonalds than working for those cheap asshats.
Other than what's been given to you here I don't think you will find any more information on this obsolete and not usually found system. As was advised, bring the phone to the demarc and see that it works properly. Then you check to see that you have a clean pair from the demarc to the jack. I'm concerned that you can draw dial tone off the digital line. Sounds like there may be a cross to a POTS line someplace.
I think you need to hone your wire troubleshooting skills. Sounds like you don't even have the proper test equipment.
-Hal
