However, these do not provide complete protection: harassers can use payphones and, in some cases, caller ID (but not necessarily automatic number identification itself) can be spoofed or blocked.
Voice over IP users may send bogus caller ID or route calls through servers in multiple countries.
Even in these cases, with sufficient law enforcement and telco effort, persistent abusers can often be tracked down by technical means.
[3] Most telephone companies have a department devoted to handling complaints regarding unsolicited phone calls.
[4] On December 19, 2018, the Canadian Radio-television and Telecommunications Commission (CRTC) announced that beginning December 19, 2019, phone providers will be required to impose universal, network-level filtering of all calls that "[purport] to originate from telephone numbers that do not conform to established numbering plans".