mentary ser- vices, reducing the business risk faced by providers of those services, should cause network demand to increase. At the same time, platform access inevitably involves a number of collateral requirements that can become sources of inefficiency and place downward pressure on network demand. For example, local telephone networks give rise to certain technological efficiencies that can only be realized if the same carrier provides both the complementary and the local telephone service. Classic examples include voice messaging services, such as voice mail and advance calling, and vertical switching services, such as caller ID, call forwarding, and call waiting, which are most efficiently provided when integrated directly into the circuit switch (FCC 1986a). The FCC eventually exempted such innovations from its platform access requirements for the simple reason that failure to do SO would have prevented these innovations from emerging (FCC 1984, 1985b, 1986a, 1996e). Platform access also necessarily requires regulators to designate the location within the network where the interface with the complementary service provider will occur, as well as the format in which the complementary service is configured. As noted in Chapter 5, the optimal level of standardization depends largely on the magnitude of the demand-side scale economies and the heterogeneity of consumer preferences. If preferences are sufficiently heterogeneous, the value that consumers derive from consuming a service that is a better match with their preferences will dominate the benefits from belonging to a larger network, in which case an equilibrium with multiple standards may well be optimal. Standardization also inevitably favors applications based on certain architec- tures. For example, the introduction of digital transmission technologies required the deployment of protocols that were not interoperable with the existing analog network. This necessitated the introduction of computer processing into the core of the network to engage in "pr