ral separation by devising a new regulatory approach that required local telephone companies to unbundle their basic services and to offer them to all unaffiliated information service providers on the same terms that they provided to their own proprietary information service offerings (FCC 1980a). The FCC expanded unbundling into a more general regulatory regime in its third Computer Inquiry. The FCC acknowledged that structural separation require- ments "impose significant costs on the public in decreased efficiency and innova- tion." These costs include precluding information services such as voice mail and advance calling, which are integrated directly into the switch maintained by the local telephone company; foreclosing the realization of economies of scope associated with joint marketing and the joint use of technology and expertise; duplication of personnel and facilities; depriving large business subscribers of "systems solutions" provided by a single company; and preventing local telephone companies from organizing their operations in the manner best suited to the markets and customers they serve (FCC 1986a). The FCC thus allowed large telephone companies to forego structural separa- tion if they complied with two unbundling regimes. The first, known as comparably efficient interconnection (CEI), was in essence a nondiscrimination regime that Networks in Telecommunications required any major local telephone company that wished to provide information services without establishing a separate subsidiary to provide unaffiliated informa- tion service providers with access to the same basic services on the same terms on which it provided its own information service offerings. CEI was to be superseded by a more comprehensive unbundling regime known as open network architec- ture (ONA), which required all major local telephone companies (even those that were not offering information services) to provide unaffiliated information service providers with unbundled access to all of their network elements (FCC 1986a).