Exactly, but if I was the lawyer defending the phonebooks, that's exactly the argument I'd make--that the PO was no different and that paying a government employee to deliver the document* shouldn't make the act any more legitimate than paying your own employee to do so. You could argue it's anti-competitive or that it's essentially a bribe to the government as well.

*Document meaning any letter, junk mail, leaflet, flyer, or phonebook.