We discuss call blockers on http://800notes.com/
often. I'm "not Michael" over there.
A few land line phones have programmable call blockers, but most don't. For those you can buy a call blocker, another piece of electronics that plugs into the phone line between your phone and the wall. They are available at Best Buy and on Amazon for less than $50.
Many smart cell phones have call blocking, or you can download a free ap. For older, dumb cell phones like mine you can put the number in your contacts list and assign it the ring tone "no ring".