I don't know where you live, but there is nothing "public" about my telephone service. I pay to have me devices connected. That kinda makes it private in my book.
I don't know where you live, but there is nothing "public" about my telephone service PErsonally I agree with people about the fact that spam is pretty annoying, but bear in mind that your telephone is analagous to a mailbox. You get shopping flyers right ? It's just another minor annoyance that has to be tolerated.