According to an article in The Seattle Times, several cell phones can be remotely reprogrammed to record conversations even when they are not on.
That's right you don't have to be on a call for someone to hear your conversation.
The article states: "The FBI converted the Nextel cellphones of two alleged New York mobsters into 'roving bugs,' microphones that relayed conversations when the phones seemed to be inactive, according to recent court documents. Authorities won't reveal how they did this. But a countersurveillance expert said Nextel, Motorola Razr and Samsung 900 series cellphones can be reprogrammed over the air, using methods meant for delivering upgrades ( like ringtones) and maintenance."
Read the entire article at: http://seattletimes.nwsource.com/html/nationworld/2003474824_bugs130.html