It radiates RF, and it causes interference to AM radio. ADSL has been around in concept for about 10 years. The idea is simple. Those same copper wire pairs that carry analog voice telephone calls can also be used to carry digital data. The voice signal uses only the frequencies up to about 4 kHz.
Copper wires have a larger bandwidth than that.
But getting from concept to practice has been difficult. First, not all telephone wire pairs are equally suited for carrying data. Loading coils and bridged taps create reflections. A continuous metallic path is preferable. Second, the distance from the central office to the subscriber is limited.