The root cause of the problem is the telcos being completely unwilling to replace ancient insecure protocols like SS7 and associated equipment. Spoofing caller

The root cause of the problem is the telcos being completely unwilling to replace ancient insecure protocols like SS7 and associated equipment. Spoofing caller ID simply should not be possible, considering the very small number of telcos that completely control network authentication, access, billing and routing. Just send everything not in your contacts to voicemail. The PSTN will be dead in less than a decade anyway. Like email, its time of utility has passed, ruined by spammers and marketers.