A network-based CLASS service of the public switched telephone network (PSTN).The feature delivers the calling number to the called line, where it can appear on a telephone set equipped with a display or on a peripheral display unit. In a call center environment, the calling number also can be linked to a database and used to access a customer profile in order to route the incoming call through an automatic call distributor (ACD) to an agent who can provide the caller with improved customer service. Calling number blocking is a feature that allows the calling party to block the transmission of CLID information on a permanent basis, or on an ad hoc basis by dialing a code prior to dialing the destination telephone number. Synonymous with caller ID. See also ACD, ANI, call center, CLASS, LEC, PSTN, and screen pop.