The Government (prosecutors at State and Federal levels) but to the best of my knowledge the Courts have always upheld defendants reasonable expectation of privacy as to landlines in the home.

I suppose pay phones are landlines, but reasonable expectation of privacy is more complicated - originally courts upheld reasonable expectation of privacy when there was a phone booth, but not when the pay phone was in the open - this varies from state to state but I would not be surprised if this expectation of privacy has whittled away in the majority of states.