Just to point out: the CAT rating has to do with the number of twists per foot. (If you look carefully next time you strip a few inches of a CAT-5 cable, you'll notice that the different pairs have slighly different twists-per-foot from each other, to reduce the cross-talk between them, too)
Until recent years, telephone cable used simple parallel conductors. In older installations, phone wiring was not pre-wired in-wall, so there was little noise pickup from nearby power wiring.
Since the wiring became the property of the building owner after the monopoly break-up, the need for noise immunity has increased with more phone wiring installations being done inside walls.
Larry
www.fineelectricco.com