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The Regional Bell operating companies (RBOC) are the result of the United States antitrust action against AT&T in 1983. After the Modification of Final Judgment, the resulting Baby Bells were originally:
Additionally, there was one comparably-sized independent (non-Bell) company of note, GTE
These companies have since merged, leaving only 4 regional telephone companies in the United States. After the 1984 breakup, part of AT&T's Bell Labs was split off into Bellcore, which would serve as an R&D and standards body for the seven Baby Bells.