A Proposal for Solving the Caller ID Problem
"There is growing concern over the interaction of VoIP systems with the legacy PSTN, and the transmission of caller identity data--most notably, Caller ID on the PSTN. It is not always possible, or obvious how, to handle Caller ID data when moving to or from VoIP and the PSTN networks. There are even business models predicated on the ability of Caller ID to be transmitted to the PSTN with a value that is not 'expected'; call centers are an obvious example, where customer-support staff make outbound calls with a Caller ID that may be from one of many possible clients. More troubling is the possibility that Caller ID may be used to trick unsuspecting call recipients into certain actions or beliefs, and it is this concern that's currently creating a legislative threat I believe must be averted."
O'Reilly Network -- A Proposal for Solving the Caller ID Problem