Depends on a number of factors: the major one is the length of the wire, but also what gauge of wire, how well twisted it is (phone wires aren't very twisted du

Depends on a number of factors: the major one is the length of the wire, but also what gauge of wire, how well twisted it is (phone wires aren't very twisted due to not expecting to use the high frequencies), the radio environment, local radio interference standards (telephone wires are leaky at these frequencies), how many of your neighbours also have DSL (although this is improving due to crosstalk cancellation mechanisms in the newer standards), how many watts the local operator is prepared to put down the wire...