ADSL is an acronym for Asymmetric Digital Subscriber Line.
This non-symmetric transmission technology allows modems, attached to standard US and Canadian twisted pair copper telephone cables, to transmit from 1.5 Mbps to 9 Mbps downstream (to the subscriber) and from 16 kbps upstream, depending on the line distance from a central exchange or from a fiber optic node strategically placed in some large neighborhood. As far as we know, there is no special telephone cable design at this time and the whole idea originally was to use the existing cable lines.
As far as X-ADSL goes, I have yet to see a proper definition of how this works and any particular wiring requirements for it. Sounds a bit experimental but I would be amazed if the telcos wanted to install new design copper telephone cables.