I assume ownership of the caller's number can be logged/checked.

I haven't had too much trouble with telemarketers lately but there is a crowdsourced app in France called Saracroche that can be easily installed on your phone and blocks spam numbers by becoming the caller id service. You can also use the app to report a number and help build the huge database.

Phone number always belongs/registered to someone?

That's where we can actually use technical solutions though: businesses shouldn't be able to place calls without cryptographically signing their origination with a key derived from their business registration.

Phone calls are essentially end to end voip these days so we have the ability to deliver that metadata.