I'm not a paranoid or conspiracy theory kind of individual, but it is good to know about these things:
FBI taps cell phone mic as eavesdropping tool
This could be exploited by anyone, not just the FBI… from the article:
The FBI appears to have begun using a novel form of electronic surveillance in criminal investigations: remotely activating a mobile phone's microphone and using it to eavesdrop on nearby conversations.
The technique is called a “roving bug,” and was approved by top U.S. Department of Justice officials for use against members of a New York organized crime family who were wary of conventional surveillance techniques such as tailing a suspect or wiretapping him.
ceo
[Image source: Netline Cellular Activity Detector website]