The Telecommunications Act of 1996 imposes certain duties upon incumbent local telephone companies in order to facilitate market entry by competitors, and establishes a complex regime for monitoring and enforcement. D is the incumbent local exchange carrier (LEC) serving New York State. Central to the scheme of the Act is the incumbent LEC's obligation to share its network with competitors. LECs were to provide unbundled access, and the new entrants could then resell these unbundled network elements recombined with each other or with elements belonging to LECs. In response to the Act, D had signed interconnection agreements with rivals such as AT&T, as AT&T is obliged to do under the act. D took advantage of the opportunity provided by the 1996 Act to enter the long-distance market (from which they had long been excluded). As relevant here, a competitive LEC sends orders for service through an electronic interface with d's ordering system, and as D completes certain steps in filling the order, it sends confirmation back through the same interface. Without OSS access, a rival cannot fill its customers' orders. Competitive LECs complained to regulators that many orders were going unfilled. A consent decree with the FCC was worked out to fix the issues. D paid 'voluntary' fines and was subjected to new performance measurements and new reporting requirements, with additional penalties for continued noncompliance. In June 2000, the FCC terminated the consent decree. P, a New York City law firm, was a local telephone service customer of AT&T. The day after Verizon entered its consent decree with the FCC, P filed a complaint on behalf of itself and a class of similarly situated customers. P alleged that Verizon had filled rivals' orders on a discriminatory basis as part of an anticompetitive scheme to discourage customers from becoming or remaining customers of competitive LECs, thus impeding the competitive LECs' ability to enter and compete in the market for local telephone service. The complaint sought damages and injunctive relief for violation of § 2 of the Sherman Act. The District Court dismissed the complaint. It concluded that P's allegations of deficient assistance to rivals failed to satisfy the requirements of §2. The Court of Appeals reinstated the complaint in part, including the antitrust claim. The Supreme Court granted certiorari, limited to the question whether the Court of Appeals erred in reversing the District Court's dismissal of respondent's antitrust claims.