Zone Usage Measurement

Zone Usage Measurement (ZUM) is the method by which phone companies in California distinguished "local" service from "long distance" service within the service area to which local phone companies used to be restricted.

Usually the local calling area includes a 13-mile (21 km) radius from the point of origination. The ZUM zone beyond that is divided into ZUM1 (12-13 mile radius), ZUM2 (14-15 mile (24 km) radius), and ZUM3 (15-16 mile (26 km) radius). Beyond the ZUM zone calls are considered intra-LATA or inter-LATA.