Engadget is pointing to a recently-filed patent application for a "call override feature" that automatically answers the phone if the caller is authorized to, in effect, turn the phone into a mobile eavesdropping device. In Engadget's words:
Sony Ericsson files patent for cellphone eavesdropping feature - Engadget - www.engadget.com:
"To some jittery parents, that voicemail rollover might as well be a death rattle when trying to check-in on their untethered teenagers. In an age of unfettered options for tracking your human of choice, it's no surprise to find a US patent filed by Sony Ericsson that will turn an unanswered cellphone into an eavesdropping device. The "call override feature" would automatically answer the phone from any flagged phone number (like that of a parent) allowing the caller to listen-in and then communicate over the phone's loudspeaker with whoever might be within ear-shot. The filing also calls for the ability to disable this auto-answer mode by entering a PIN which would allow parents to always monitor their kids while grandma could still whoop it up at Bingo without her handbag shouting "Ma, you ok! MAA!?" Seems something like this is just going to create more problems on that slippery-slope of control than it will assuage given spotty coverage, tech-savvy teens, forgetful elders, and any number of valid reasons to be disconnected."