Don't everyone answer at once! I'm posting back to convey that I found out what the problem was in case someone else encounters this scenario. After returning to the site, I determined that there was something about the white/blue pair that the system didn't like. I could get dial tone across it with a butt set with no problem, all of the usual continuity testing passed, but once a digital set was connected, the pair didn't work for audio. After moving to another pair, it worked fine.

What's odd is that I only had a three pair cable to work with and the third pair was being used for a fax. I put the fax on what was the "defective" white/blue pair and it works perfectly fine.

Ed Vaughn, MBSWWYPBX