Phone Tap

I heard he can not. Why not? Its seems that if someone agrees to something for a call from the tap, it would be able to be used in court. What is the use of a phone tap?

Yes, the evidence obtained using a wire tap law under a valid search warrant may be used against you. Or if the tap wire is placed on your phone under the Patriot Act.

In some states (Texas), it is illegal to place a tap on a phone, so if you save your step-son of plotting to shooting yourself in the stomach and watch you bleed to death which may be used to acknowledge of a crime and you could be looking up to 20 years in prison. The fact that you've turned the tape to the police, to avoid the shock to kill you might not be persuasive to the prosecution (persecution) lawyer.

Only if the wiretap was authorized by a judge to sign a warrant.

Yes, it may be you havn't watched CSI

Assuming that the wiretapping was approved by a judge, then yes it can.