I speak of the National Do Not Call Registry. Ever since they implemented the registry, my telemarketer call volume *has* gone down. Like cockroaches, though, teleslime somehow manages to squirm back into the house.
Two big loopholes allow them to do so -- if they are a charity or a political figure, they can freely ignore the list. Same with businesses you already have a relationship with, like your phone company or your bank.
Of course, many banks, phone companies, credit card companies, etc., are perfectly willing to whore out your phone number to the highest bidder so they can call you as a "preferred partner" and get around the no call list.
I've found a way around it though... and had some geeky fun in the process! I grabbed an old Pentium III PC that I had laying around, downloaded a copy of TrixBox (formerly known as Asterisk@Home), and picked up a phone line card made by a company called Digium, and lo and behold, I set up my own PBX switch! Just like the office! Woo hoo!
...ahem...sorry. Got a little excited there. What is TrixBox, you might ask? It's a live-cd installation of the Linux-based Asterisk open source PBX switch.
What does all that get me? Well, for starters, a really nice voicemail server. See, where I live, my local phone company doesn't offer voice messaging (c'mon Qwest, I'm not exactly in the boonies y'know?), and I *hate* those stinking $20 digital message recorders. They sound like the caller's talking out of a toilet. The darn thing will even do VoIP if you want to try your hand at Internet-based telephony.
Back to my original topic, though... I also get a really nice blacklist filter as well. Tired of a particular telemarketer bugging you? Just pick up the phone, dial a special code followed by the teleslime's phone number as listed on the caller ID, and voila! They get a recording instead of the call ringing through to interrupt your dinner.
You can do a number of things with a blacklisted call, like drop it to a voicemail box, or you can simply send them to a message that tells them they aren't welcome, or you can even make them listen to evil screeching monkeys if you prefer... (muwhahaha...)
You can handle calls without any caller ID the same way, although it's probably better to just route those to a voicemail box in case it's a legit call.
I have under $200 invested in the add-on card to hook it to the phone line - the software's free and the PC is an old one that had been replaced in my last upgrade.
Mind you, this is not a project for the weak-hearted luddite, but if you're comfortable tinkering with PCs this one may be worth a look.
You can find a really good howto for TrixBox out on Nerd Vittles.