"Cell phone users, beware. The FBI can listen to everything you say, even when the cell phone is turned off. [snip] Experts say the only way to defeat it is to remove the cell phone battery. [snip] "Any recently manufactured cell phone has a built-in tracking device, which can allow eavesdroppers to pinpoint someones location to within just a few feet,"
CNET News December 1, 2006
"The U.S. Commerce Department's security office warns that "a cellular telephone can be turned into a microphone and transmitter for the purpose of listening to conversations in the vicinity of the phone." An article in the Financial Times last year said mobile providers can "remotely install a piece of software on to any handset, without the owner's knowledge, which will activate the microphone even when its owner is not making a call."
""If a phone has in fact been modified to act as a bug, the only way to counteract that is to either have a bugsweeper follow you around 24-7, which is not practical, or to peel the battery off the phone," Atkinson said. Security-conscious corporate executives routinely remove the batteries from their cell phones, he added."