On the National Do Not Call list already. If they actually have a do not call list and care about such things then they should comply with National Registry first and foremost. They dont so why encourage them by calling them back at all?
Phone rang, did not answer, message not left on answering machine. I will not answer phone calls that I do not know who is calling. So for all of those 800, no call id available, caller unknown, etc. YOU ARE WASTING YOUR TIME DIALING MY NUMBER.