Wiretapping A.K.A. "bugging" is actually not a "physical invasion." This act can be conducted without a warrant as long as the people conducting this act have lawful evidence that this is something that is needed.
If police want to wiretap someone's phone they can as long as its not in an enclosed area and is a private call. If both of those happen then they need to have a warrant before anything further is done. This is also called lawful interception.