Who is authorized to tap your cell phone and how?

Answer 1

This is a very controversial issue. The only people that can really tap your cell phone legally are the FBI, CIA, NSA, or the police. If you have done something illegal lately and it is severe enough, you may not have been contacted by the police, but they may be watching you. Scary huh? Watch what you say.
Though cell phone tapping is very rare unless you are a suspected terrorist or felon, you may still be subject to it if they bring the information that they have gathered about you saying that they believe that you may be a suspect and that if they bring forth good enough information, good enough to make the judge convinced that you may have done something, then he may grant a search warrant, or phone tap warrant, allowing them to tap your phones, legally.
HOWEVER, without a warrant from an actual judge, and they try to use that information in court, they (the police) may be subject to criminal charges, and indisputably the information will be invalidated. You can sue for this also.
Well i hope this answers your question and i hope this helps!!

Answer 2

Legally, only law enforcement agencies and the government with a court order. In real life, anyone who can get a hold of the proper equipment, and know how to use it can tap your phone line. If you watch what you say, you will NEVER have a worry on who is listening.

Answer 3

The government and all it's known and secret agencies. They are everywhere, just waiting for you to do or say something seditious. So, watch your back, buddy.