The practical implementation of this (at the time) was ADSL, HDSL, IDSL, and SDSL. Those technologies all took one or two copper pairs, and terminated them on a DSLAM (or similar device in the case of HDSL) instead of on a telephone switch. For physical pairs connected to an analog voice port on a telephone switch, between the band pass filtering and DSO coding, you were never going to get more than 56kbps. The xDSLs could get between 144kbps to a several mbps in practice, depending on the variant and line conditions.
Keep in mind that at the time, LAN speeds over controlled twisted copper pairs over short distances (100m) were 100mbps - 1gbps.
If you've ever seen the physical condition of the telephone company's outside subscriber wiring (what they call "outside plant") -- and particularly the intermediate splices between central office and subscriber -- you would quickly disabuse yourself of the notion that you could transmit anything close to 1gbps over a twisted pair.
Keep in mind that at the time, LAN speeds over controlled twisted copper pairs over short distances (100m) were 100mbps - 1gbps.
If you've ever seen the physical condition of the telephone company's outside subscriber wiring (what they call "outside plant") -- and particularly the intermediate splices between central office and subscriber -- you would quickly disabuse yourself of the notion that you could transmit anything close to 1gbps over a twisted pair.