In the early days of fighting email spam, that was enough. Every network operator was responsible for receiving spam complaints and responding appropriately. Network providers that couldn’t or wouldn’t prevent spammers from using their networks were blacklisted and other networks would refuse to route mail originating from them.
It wasn’t perfect, but it was far better than nothing.
I'm curious - is this available in a call passed through twilio ?
I would like to log, or pass, the prior network hop using twiml ... or a twilio function, I guess ...
Distrusting one of them and the calls that come from them is something of a non-sequitur since you chose them and intentionally became one of their customers and pay them to receive those calls.
TL;DR This isn't like email or IP traffic where you're interacting with other IPs in a purely untrusted network model. Merely analyzing the previous hop doesn't tell us anything valuable.
This assumes that is that there isn’t some kind of international treaty that forbids doing so. The existence of such has been claimed from time to time in similar discussions but I have yet to see an actual citation.
That's wrong, phone signalling systems always specify the originating number and it cannot be spoofed. The key thing is that only 911 responders and similar lines have the CLIRIGN flag set on their lines which means that the spoofed number transmitted via CLIP is ignored and the real one used instead.
In addition victims of e.g. threat calls can have the MCID flag set on their line which makes the provider systems log all call information for later retrieval by police.
I would also bet that there are regulations that require phone providers to complete all calls that are presented to them.
My provider, T Mobile, does overwrite the caller ID with “Scam Likely” for what they believe to be telemarketing calls, which is probably the best they can do until we implement a standard that authenticates the origination ID of calls.