I don't really like the idea of more regulations and more potential ways to get sued, but I do like the idea of less spam so how about these steps in this direction:
-Get rid of the government Post Office. Allow free competition while enforcing property rights (delivery without consent is trespassing/littering). Depending on the interplay of new competition and the Post Office's current capacity to price services correctly maybe the price for these types of mailings goes up and they become less common.
- Perhaps part of this new competition involves mail delivery services that as a way of getting your service (you having a mail box that allows their company to put things in) they filter this junk out for you.
- Make it clear under what terms delivery services are allowed to put things in your mailbox, anything else is littering or something. I don't know if you can currently refuse large amounts of junk mail from the USPS, but if more people put this junk in a huge box and left it out and the deliverer was required to pick it back up perhaps that would cut down on this. Make refusing to similar to litter.
On the landline side, perhaps tech solutions like phones that hook into the data from Report Spam in Google Voice can help there. Or more deregulation in phone service so there are more suppliers that offer blocking spammers as a feature.