The Do not call Registry list is just as it implies..... simply a list.  A list that is based upon the honour system.
It was never intended to do anything more.  Just like bank robbers,  car thieves,  muggers,  and hookers,   there will always be those who will violate it and do not care.   Keep in mind that any common carrier..i.e. telephone companies, can consider you a customer because at some point,  if you have used a telephone to call or receive calls,  it is most likely that you passed through lines or facilities of all such carriers.  If you use a cell phone,  your calls will pass thru common towers and repeaters accessed by various carriers.  "Doing business with"   does not end with the one that you are directly accessing,  but extends to each and every link in the process of providing that service.    No I don't agree with that,  but this is what an AT&T  security rep. supervisor told me when I complained about them charging me $5  to block unwanted numbers.  And I agree that the DNC should be Sh/tcanned since there is no way that it can function the way that everyone expects it to.  It has lived beyond it's functioning purpose.  It's sole purpose for creation and existence today, was and is to limit the number of Telemarketing calls from legitimate and Registered with the FTC Businesses.   When it was conceived,  we did not have all of the scamming,  spamming scum that we are dealing with today.   I would suggest to any and all,   if you are not satisfied with all of those actual legitimate companies who are honouring the DNC by not calling,  that you call the FTC/DNC  post haste,  and cancel the service.   That way,  it can no longer be held accountable for everything from the Great Biblical Flood to present day Herpes.