All of those old crime movies will need to be rescripted-nowadays there is no need to keep dangerous criminals talking on the line, for what seemed like an eternity to theatre audiences, in order to trace their whereabouts. Ever since the telephone networks were digitalised in the 1980s, the caller's number is transmitted with the call, which means that the recipient's handset can be made to display the number prior to the call being accepted.
Although it is possible for private individuals to apply to override this feature and have their number withheld, this facility does not work for calls made to the fire service, the police or the ambulance service. Malicious Call Identification (MCID) enables a recipient to mark a phone call as malicious, and then the phone system will automatically trace its source. More detective work is required only if a call was made form an analogue telephone, or through international networks, such as companies that specialize in providing cheap calls.