that receives any revenue even though the network that terminates the call also incurs costs. Some mechanism for compensating the terminating carrier for the costs it incurs would thus seem reasonable. In recent years, there has been growing interest in "bill and keep" arrangements, in which each network recovers the costs of terminating traffic received from other networks. Bill and keep arrangements have long been a common way to handle interconnection between independent telephone companies and the Bell System, and the 1996 Act specifically provides that its reciprocal compensation requirement should not be construed to preclude bill and keep arrangements. Indeed, the FCC has opened proceedings to consider whether it should adopt bill and keep as the sole basis for reciprocal compensation (FCC 2001d). 4. Platform Access Mandated platform access requires that a firm's network facilities conform to a stan- dard that allows other companies to provide complementary services. We define a platform as a collection of related technological standards. In telecommunica- tions networks, platforms permit compatible transmission of communications and interconnection of equipment. In computers, a platform is a "reconfigurable base of compatible components on which users build applications" and is identified with "engineering specifications for compatible hardware and software" (Bresnahan and Greenstein 1996, p. 7; see also Greenstein 1998; Bresnahan and Greenstein 1999). For example, IBM devised standards for the personal computer that were adapted by manufacturers of components and software designers. In turn, software design- ers use Microsoft's standards for personal computer operating systems to create applications that are compatible with its operating systems. When standards are widely available and not necessarily proprietary, indepen- dent companies can produce complementary components, which in turn allows consumers to assemble groups of products. In information technology, the IBM standard allowed a modular set of