Whereupon Justa Lurker responded:
Or even a "carrier's carrier's carrier."
Back in the 1980s, Wiltel provided capacity to Norlight, which in turn provided capacity to IXCs. At the time, Norlight was owned by a consortium of Minnesota- and Wisconsin-based electric utility companies. Most of the network was constructed using grounded Optical Ground Wire (OPGW) installed at the top of the electric transmission lines owned by the member utility companies. OPGW is a metallic (usually aluminum-clad steel) conductor with optical fibers buried inside; it is installed at the top of a transmission line in place of a static wire, where it serves the same purpose as the static wire -- protecting lower conductors from lightning.
Commonwealth Edison Company. ComEd was not a member of the consortium that owned Norlight, so it had no financial interest in Norlight's success. ComEd's price for letting Norlight use its transmission lines was higher than Norlight was willing to pay.
So Norlight turned to Wiltel instead. Wiltel (then a subsidiary of Williams Pipeline, a gas and petroleum transmission company) installs fiber optic cables in abandoned pipelines. Norlight contracted with Wiltel for dark fiber between Maple Park IL and Chicago, bypassing most of ComEd's transmission lines.
Thus, Wiltel became a "carrier's carrier's carrier" (and AFAIK, it still is, although since I've retired I've lost contact with the folks I used to deal with).