Length doesn't specifically matter, as it's technically going over hundreds to thousands of feet of copper already on Verizon's end of the plant. Sometimes distance of runs does make a difference though if using low quality cable or in marginal situations. But typically, look for some twisted pair/CAT3 grade Cabling as you want something not too thick or too thin that could weaken/noise up the signal.. Don't use the flat telephone extension cable as that cabling doesn't have the kind of noise isolation DSL ideally runs with. Take a look at the supplied cable the modem came with for what I'm looking at. That is two-pair CAT3 grade cabling.
