I work for a telco, though not in that department. We put a lot of effort into trying to block spam calls, and adapting systems to the newest tricks. The reason why the results aren't better is (I'm being told) a combination between IP telephony making reliable source tracing all but impossible, and common carrier laws which mean that you can't block a call unless you're 100% certain it's a scam, otherwise you open yourself up to being sued.

I imagine that many of us would gladly accept blocking call with a much lower certainty. Maybe we need an audio catcha.

Thank you for the insight.