It's fairly difficult to stop robo dialers. I used to handle about a billion calls a day for providers. Robo calls had to go on separate connections and had other limits and higher prices than regulal ("conversational") calling.

But many customers would slip in lots of dialer anyways. You can tell after the fact, by looking in aggregate. But on a per call basis, nope.

Now, we tried blocking repeated caller numbers. Spammers would just switch to using random numbers. For many reasons (some good) it is simply not tractable to know if s number is s valid source for a call. It's vastly more complicated than say IP spoofing.

The most effective solution is to have an answering service/program that screens calls and allows known callers without further hassle.

Your provider could offer a service to block "known" bad numbers, but a lot of business use the same number for many things. I'd be surprised if some consumer services don't offer such services. Though, there may be some regulations that require them to attempt to complete the call.

Also note that some dialer, like political calls, are expressly allowed and don't have to follow do not call.

The best recourse you have after the fact is to make an FCC complaint and persue it. I've seen tons of complaints that go nowhere because no end user pushes the issue. For really illegal dialer, there's gonna be several intermediaries, say, 5+ isn't surprising. Each one has to escalate to the next. Without a fire under their ass, most providers will close the complaint with effectively "can't repro, dunno".

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 grew up in Ireland. Very few robo calls. Why? It's illegal.

The solution is not a technical solution, but a legal one.

Sure. It's mostly illegal in the US,too. But the FCC simply doesn't pursue the matter enough. Even in illegal things, like guys that setup a line pretending to be the IRS, the worst that happens is someone cuts some little account off.

It could be different. And as a carrier, I've begged other carriers to push. Have their end user escalate. Get LE involved and get them to go all the way till they find the originator of calls and nail em. But out of the few hundred "complaints" I've seen, only one or two even pretended to care, and none ever really followed up.

The US could kill illegal robo dialing, at least a lot if it, just by getting serious and slapping fines down.

It's so dumb, that even the FCC put out a prize for the best anti robo dialer tech someone could come up with. It defies explanation.

We do have a very strong law, the TCPA, that prohibits robocalls to cell phones without prior consent, with a private right of action and a $500-$1,500 _per violation_ (per call at least) penalty. It won't do you much good against scammers, but against actual businesses with assets that could be seized if necessary, it's awesome.

(I personally sued a debt collector in small claims court for wrong number robocalls to my cell phone, and settled for the entire amount I was asking, $500 per call.)

Yes there are 2 kinds of illegal: de jure and de facto. You need it to be illegal both way.

A network that allows anonymous agents to spoof their address is absurdly broken. yes, there are legitimate technical reasons for that problem to exist, but they've had like a hundred years to figure out how to fix them.