Use the plastic sheathing around the phone wires as a waveguide. With 1,000x more spectrum, you get 1,000 more speed. Glass fiber optic waveguides can carry 250 terabits. John Cioffi wants to apply similar techniques using the air gaps between the plastic surrounding a billion phone lines.
The proposed terabit DSL can use 300 GHz+ of spectrum, "submillimeter waves." Current DSLs use 100-500 MHz. Higher frequencies just wouldn't make it through a standard copper wire. The signals get weaker (attenuate) very quickly in copper. 500 MHz can only carry about 30 meters. Gigahertz, even less.
Cioffi proposes using the tiny air spaces between the plastic insulated wires as a "waveguide." The signal would travel over the air gaps, not the copper or plastic. Fiber optic, glass or plastic, "guides" the waves; why couldn't the plastic insulation do similar? (The waves are very, very small. They can easily fit in the gaps.) The signal is carried through the air between the wires, not on the copper wires.