I think the limit is about 18,000 feet. Then you might have trouble
> carrying DSL over it ...
Correct, but that's the approximate limit for the total length from the switch to the telephone. Beyond that, the signal is typically attenuated too much, mainly by cable resistance, and gets buried in noise.
As someone else has pointed out, you need decent cable, routed clear of sources of interference (such as power cables and cordless phones), otherwise interference will be a bigger problem than loss of signal.
Phil McKerracher
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