Call centers can be broadly defined as facilities designed to support the delivery of some interactive service via telephone communications (Gans, Koole, & Mandelbaum, 2003). Applications include among others telemarketing, customer service, help desk support and emergency dispatch. In most cases, the primary function of a call center is to receive phone calls that have been initiated by customers. Such operations, known as ”inbound” call centers, are the topic of the present paper.