Most cell phone companies let you black list calls preventing them from calling you ever again. Verizon, my carrier, limits the free blacklist to some low number (5 or 10) and after you've exhausted that you can pay a small monthly amount to let you add as many as you want. This credit card number is persistent, their "machine" is not bothered by no answers or hang ups, it will simply retry as many times as it's been programed to. That gets me back to black-listing. If you black list they think they have dialed a disconnected number no longer in service and since they don't want their machine churning on those it gets eliminated programmatically. In theory then, after you've listed a number and left it there a couple of months you could replace it with the number of a newer pest and save the cell company's fee for an unlimited blacklist.
Dean - this was great information and advice. I just text'd this 206 number to AT&T and will look at my bill tonight and see the pests to block. Again, great info!!