I'm going to have to strongly disagree with this one. Can you imagine the evidence from the wiretaps say, on OJ, Casey Anthony, Scott Peterson, etc. They would have had to come up with a secret language to speak with their attorneys - or in person and not over the phone ever - if this were allowable.
Any conversation Scott Peterson had with his attorney about his case would not have been admissible at trial. But LE also did arrest him when they thought he was fleeing to Mexico.
JMO