[CardsFan]

I've been using "NoMoRobo" in conjunction with my AT&T landline for several months and pretty happy with it. Numbers that are known to be bogus will ring once and be disconnected. If a call gets through, enter the number on their site and usually within 24 hours it will be blocked from there on out. It's free for landlines.

It has drastically cut the amount of B.S. calls I get through the day. If phone rings just once, I know I can ignore it.