The Financial Times of the 2nd August 2005 [page 4 of the UK edition] reported that the UK police can ask mobile phone operators to download special software to your phone without your knowledge or permission. When this has been done the police can turn on the microphone of your mobile phone whenever they wish and listen to any conversations in your vicinity. This works whenever your phone is turned on. You do not have to be making a call. One assumes a similar capability exists in other countries.
The story was also picked up by the UK Guardian newspaper, from which this quote was taken. "The main means of tracking terrorist suspects down has been the monitoring of mobile phone conversations. Not only can operators pinpoint users to within yards of their location by 'triangulating' the signals from three base stations, but - according to a report in the Financial Times - the operators (under instructions from the authorities) can remotely install software onto a handset to activate the microphone even when the user is not making a call."
In 1759, Benjamin Franklin wrote: “They that can give up essential liberty to obtain a little temporary safety deserve neither.”