 tendency of monopolists to charge prices that are inefficiently high has long led state and federal agencies to regulate the rates charged for tele- phone service. The standard regulatory instrument employed to regulate telecom- munications rates is the tariff, which in the case of intrastate service is overseen by state agencies commonly known as public utility commissions and in the case of interstate service was historically administered by the FCC. The tariffing process begins when telecommunications carriers file schedules containing all of the rates, terms, and conditions under which they will offer service. The agency then reviews the proposed rates to ensure that they are "just and reasonable." Once the tariff has been approved, the carrier must offer service under the terms specified by the tariff on a nondiscriminatory basis to any requesting party that qualifies to receive Network Regulation Basics the service. Under the so-called filed rate doctrine, the tariffed terms constitute the entirety of the contractual agreement between the customer and the carrier and displace the terms of any private agreements. 13 The Supreme Court has called determining whether a particular rate is rea- sonable an "embarrassing question" (Smyth V. Ames, 169 U.S. at 546) as well as a "laborious and baffling task" (Mo. ex rel. Sw. Bell Tel. Co. V. Pub. Serv. Comm'n, 262 U.S. 276, 292 (1923) (Brandeis, J., concurring in the judgment)). One of the central difficulties has been how to determine the reasonableness of any particular rate. The difficulty of this determination is best summed up by Justice Brandeis's classic concurring opinion in Missouri ex rel. Southwestern Bell Telephone Co. V. Public Service Commission. Brandeis recognized that the most accurate methodol- ogy for determining the reasonableness of a proposed rate would be to compare it to the prices charged for comparable products bought and sold in an open market. The problem was that "utilities, unlike merchandise or land, are not commonly bought and sold in 