reply to Sven Bjork
Use whitelisting. My phone never rings unless it is somebody I want to hear from.And the IVR requires the caller to press 7 if he wants to leave a message, so robo-calls do not clog up my voicemail.
This thread is a good lesson on the value of an IVR. Trying to filter therubbish without one is like being a one-legged man in an ass-kickingcontest.