What makes them private? They're operated on the phone company's lines and by talking on their lines you're compelling them to carry certain speech. The logic that states private communication carriers have an unlimited right to ban what they want to on their networks leads to the conclusion that "private" phone calls can be censored.
It isn't wire-tapping if they block you from accessing the wire to begin with. Forcing the phone companies to carry your speech over their wires is compelling speech across their property which should be against their 1A rights if you're correct. However, it clearly has been ruled not to violate their rights.
I mean, there's a law against it. But there is a lot of known warrent-less wire-tapping, both by govt and industry, and everyone shrugs.
And it's not even a de jure vs de facto thing, since by now a lot of the ostensibly illegal stuff has been either defended successfully in courts or buttressed by the govt.
