There's a similar thread here about extending a T1 over a short CAT3 cable; so this is a bit redundant. But I did a site survey where the client had a new, unused 50-pr CAT 3 from the demarc in the basement to his 2nd flr suite through smurf tubing and wanted to have a new DS-3 extended. I'd estimate it would be about 350 ft from A to Z. His existing T1 had been separately run over CAT5 within the same smurf tube as the 50-pr, but I wondered if that was a lot of labor for nothing. After all, a copper pair is a copper pair, right? Wouldn't a DS-3 function fine if extended over CAT3?