T odd Zywicki defends the do-not-call registry from attacks by libertarians and small-government conservatives:
I believe the criticism is misplaced--the DNC registry is simply law & economics in action. It took an ambiguously defined property right (when can telemarketers call you), defined it clearly (telemarketers can call you whenever they want to), and provided a low-cost way of reallocating the property right (register on the DNC). Thus, it is nothing more than the Coase Theorem in action.
But even more, the DNC is actually the first example I can think of that illustrates a Contracts principle of an efficient minoritarian default rule. Usually contract default rules are allocated so as to create a majoritarian default rule (i.e., what the majority of people would want). Based on the registration numbers, a majority of Americans want to be free from telemarketing calls. So why not make the default rule "no calls" and make the telemarketers get your permission? Leaving aside the logistical problems (Would calling you to ask you if you want to be called count as a telemarketing call?), the minoritarian default rule is efficient because the transaction costs of reallocating are so munch lower for consumers than for telemarketers, especially because the FTC made registration so easy.
If you're wondering what the Coase theorem is, go here.