I think the point is that there is a distinction between calls that are intrusive spam or arguably scams but not already illegal, and calls where the content of the call is itself unambiguously illegal.

Bans on unsolicited calls, or do-not-call lists, can be effective for the former, as it moves the behavior from being legal to being illegal, while for the latter, they are already breaking laws, and technical measures or enforcement are more important.

100% agree. When I said scam above, I meant the obviously illegal fraudulent scams (like the "We're MS, and see you have a virus, please give us your CC info and let us remote into your desktop" stuff).

Because I'm on the DNC list in the US, I don't get many/any legal telemarketing calls.

The political stuff is really annoying because very little of it is directly from the campaigns themselves. It's all push polls and PACs and whatnot.