I've been thinking about running my own in-home PBX to deal with this, too.
Whitelisted numbers, friends, family, and businesses I want to talk to: Rings right through.
Numbers not on the whitelist: straight to voicemail, my phone does not ring, not even once. The voicemail says, "Hello?" a few times to see if anyone answers, then says "This is a recording, please leave a message" in order to (presumably) get the robo-calls routed to an actual agent.
Numbers on the blacklist: Forwarded to Lenny, or something very special I program myself. (I don't like that "Lenny" says "Yeah" and similar positive type words from time to time; those crooks might claim that was an agreement to get a subscription to The Wisdum of L. Ron Hubbard crammed onto my phone bill.) My ideal would be to sound perfectly normal, do some interpretation of what they're saying to actually address things they say, and do a "curious about the product but not agreeing to anything" act for as long as they stay on the phone.
On the top of the blacklist are those evil <redacted> who call six times simultaneously, so the phone rings a whole lot longer than normal before going to voicemail, and the Caller-ID announces their name six times. Bastards. This is the sort of thing that makes me yearn for the "Scanners" power to reach down the phone line telekinetically and set their computer on fire.
Bonus, custom voicemail messages for appropriate callers, white/non/blacklisted. Like "Hi, Mom, we're not home, call my cell."