ed. 17 Under its revised rules, the FCC mandated that entrants should still be able to obtain virtually all of their facilities at wholesale regulated rates from their rivals, the incumbents. 18 The economic justification for requiring incumbents to share their facil- ities with entrants is that some capital facilities cannot be replicated eco- nomically by entrants. The economies of density or "fill" may preclude the Opening Telecom Markets: The 1996 Telecommunications Act duplication of network facilities such as conduits, pole lines, and wires. But the act failed to refer to "essential facilities" or to "natural monopoly." Rather, it suggested that anything that entrants needed to fulfill their busi- ness plans should be made available if the absence of such wholesale offer- ings "impaired" their ability to compete. Hence the FCC dictated that the "local loops," the wires connecting the subscribers' premises to the telephone companies' switching facilities, be unbundled and made available to competitors. Central office switching, the transport facilities between the companies' offices, numbering re- sources, network intelligence, and operating and support systems also had to be unbundled SO that an entrant lacking the wherewithal to build its own facilities could compete. Furthermore, incumbents had to share the individual copper loops that terminate in a subscriber's premises, thereby allowing an entrant to lease the upper frequencies on the loop SO as to be able to provide high-speed, broadband Internet service without having to provide ordinary telephone service. This "line-sharing" requirement came a few years after the commission's initial 1996 unbundling rules, but it was overturned by the U.S. Court of Appeals in 2002 in a decision that also asked the FCC to reconsider its approach to unbundling once more. 19 The 2002 reversal sent the entire unbundling regime back to the com- mission for a second time. As a result, seven years after the passage of the 1996 act, one of its most important provisions was 