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.
> I assume ownership of the caller's number can be logged/checked.
Alas, last time I checked numbers were something that was announced in-band, so it could be trivially faked by the caller. But I'm not sure if that's still true.
Not in the domain at all but wasn't this the purpose of STIR/SHAKEN but the biggest blocker was that large telcos hadn't deployed it? I think Android and iOS dialer app show you whether there was Caller ID Verification done or not so you may be able to drop anything unverified.
In France, thanks to STIR/SHAKEN, this is not possible any more for the fixed phone numbering plans (and telemarketers have to register their phone numbers in a subset of this numbering plan). For mobile lines, this is still not 100% implemented due to the difficulty of handling roaming, but I think it is becoming efficient as I didn't have a telemarketer with a mobile number since a long time (they seem to hide their number now).
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.