The telephony protocol permits owners of a local telephone exchange (any setting with many internal phones) to display a chosen number in the caller-id field. T

The telephony protocol permits owners of a local telephone exchange (any setting with many internal phones) to display a chosen number in the caller-id field. The intent was that outgoing calls would appear to come from the general number of the organization, rather than the individual who actually placed the outgoing call. Unfortunately, when this was designed, no thought was given to the possibility of (now widespread) abuse. One cannot completely blame the original designers: when they did their work, telephony was essentially a closed system controlled by a handful of large telephony companies. The rise of using the internet as a transport medium was not something they could have anticipated: there was no internet back then!