I have a very simple and effective method to get rid of cold callers. As soon as I establish that the person phoning me is not someone I know or is not someone who I asked to phone me I just press the little red hangup key on my phone and don't feel bad about it at all. I never asked them to phone me and I know I am am not interested in their "amazing offer" so I feel nothing to just cut them off mid sentence! It actually makes you feel a little good afterwards.