In the UK there rules about spam calls too, however most of the calls my parents get are international numbers. I told them just to ignore them, but they got upwards of 5 calls a day so it was pretty annoying.
I setup a PBX so that I could block any repeat callers, but that didn't really work because each call is from another random number. There were also a few automated calls so I set it up to play an automated message of 30 seconds saying to press a code to speak to someone, if the number is withheld or international. That ended up blocking pretty much all the calls. I guess the dialers interpret it as a voicemail greeting and move on.
I've since found out there are plenty of SIP providers who if you ask them nicely will let you send any callerid without proving ownership - even for international calls. When it costs them around half a US cent per minute (probably less in bulk) it's not surprising there are so many spam calls.
Another good technique to reduce the number of robo calls is to have your PBX answer immediately, and play a fraction of a second of the "number unobtainable" tone, which is enough for many greedy "robo's" to give up and move on where as a human will barely notice.
Providers have to take calls without ownership. It's simply not feasible otherwise. Sometimes, I'd be handling calls going from one landline neighbor to another. There's just too many intermediaries.
Now, for small, low volume deals, like say, Twilio, yeah you could force an ownership test. But it would have no impact on the real offenders.
I setup a PBX so that I could block any repeat callers, but that didn't really work because each call is from another random number. There were also a few automated calls so I set it up to play an automated message of 30 seconds saying to press a code to speak to someone, if the number is withheld or international. That ended up blocking pretty much all the calls. I guess the dialers interpret it as a voicemail greeting and move on.
I've since found out there are plenty of SIP providers who if you ask them nicely will let you send any callerid without proving ownership - even for international calls. When it costs them around half a US cent per minute (probably less in bulk) it's not surprising there are so many spam calls.