Junk Calls

Is anyone able to explain to me why, in 2007, we are not able to program "junk caller" numbers into our phones much like we do with e-mail? I'm not talking about an ineffectual 'no call' list whereby marketing companies that happen to belong to a certain organization supposedly won't call me. I don't want to go through the hassle of contacting people to get my name off lists. I also don't feel like I should have to release information about myself in order not to be bothered. I just want the functionality to say 'this phone number cannot call me' on the fly. Would this be hard. Does it already exist?