Earlier quoted context omitted.
Dialup modem did the same thing but with more efficient protocol and error control via a network stack. ADSL also took a step further and used the shielding on copper cables to attain higher (inaudible) frequencies. The tech in some form is still about this is just the granddaddy version :D
ADSL does not depend on shielding of copper. It uses Discrete Multi Tone modulation which modulates many subcarriers to be able to compensate for channel distortion as the characteristics of each phone line are rather different in the frequency domain. This same technology underlies many modern wireless protocols as well.
That might have been my misunderstanding. I had a (PhD) friend doing research for BT in the mid 90s in DSL technology (which hadn't been invented then, it was ISDN only) at Lancaster University UK, and he told me it was using shielding. Perhaps I've got it confused with a competing technology he was looking at at the time.