Privacy: Phone tapping & the such

Taken from Wikipedia on "Telephone Tapping"

Telephone tapping is officially strictly controlled in many countries to safeguard an individual's privacy; this is the case in all developed democracies. In theory, telephone tapping often needs to be authorized by a court, and is, again in theory, normally only approved when evidence shows it is not possible to detect criminal or subversive activity in less intrusive ways; often the law and regulations require that the crime investigated must be at least of a certain severity. In many jurisdictions however, permission for telephone tapping is easily obtained on a routine basis without further investigation by the court or other entity granting such permission. Illegal or unauthorized telephone tapping is often a criminal offense. However, in certain jurisdictions such as Germany, courts will accept illegally recorded phone calls without the other party's consent as evidence.

In the United States, federal agencies may be authorized to engage in wiretaps by the United States Foreign Intelligence Surveillance Court, a court with secret proceedings, in certain circumstances.

Under United States federal law and most state laws there is nothing illegal about one of the parties to a telephone call recording the conversation, or giving permission for calls to be recorded or permitting their telephone line to be tapped. However the Telephone recording laws in some U.S. states require only one party to be aware of the recording, while other states require both parties to be aware. It is considered better practice to announce at the beginning of a call that the conversation is being recorded.

Are there any instances in which phone tapping should be legal? Why or why not?