It was the result of antitrust regulations only inasmuch as it caused the government to begin legal proceedings against AT&T. It isn't the result of antitrust regulations in the legal sense, just the result of those antitrust regulations existing because had they not existed then there would be no case against AT&T and therefore no settlement. But those results were not an instance of antitrust regulation legally occurring. Certainly not within the sense I initially referred to it which was a regulation such that it could still be used today ("I thought GGP was referring to a real regulation that was later removed"). We can call the AT&T case a "one time regulation" in that it is not a law but was still carried out by the government even if technically optionally accepted by AT&T. But this is certainly different from a "real" regulation which is a written rule that takes affect every time the conditions of the rule are met, which was not the case in AT&T.