If you use a VoIP service like Twilio and voip.ms, you can set up a very simple IVR menu that just asks unknown callers to press 1 to be connected to you. No AI involved.
For me, this has been surprisingly effective against robocalls. Obviously this isn’t going to work against scammers who call directly, but most of the spam calls I receive start with some pre-recorded message which isn’t going to pass the menu.
Edit: s/auto/pre
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