[PaybackTony]

This actually isn't true. I build telecommunications software and although individual carriers may offer a binary true or false response to a DNC request, the actual DNC list is a csv of all the numbers in a given region / area code that are on the list. You must pay for access to the list, per area code or you can pay a larger fee for all area codes. From experience, this is why many telemarketers don't obey the DNC list. They want to, but they also don't want to pay the greater than $15k it costs to access all area codes' DNC list. You're also not allowed to resell access to the list in any way, so any service offering a scrub against the national DNC is violating those terms. Most services that say they do that still require you to give them your DNC access info (SAN).

The pay to access part I think is what separates it from the IP Address list here.