The solution to the junk phone call problem is to have the ability to charge the caller money in order to be able to make your phone ring or leave you voice mail - even if you don't answer. I as the recipient of your call can choose to refund the money back to your account if I decide your call was legitimate; if not, I keep your ante. I can also set the amount I charge for you to call me - which can be anything from $0.00 to $1,000,000.00.
If such a system were in place, junk phone calls would disappear overnight.