The Bad News...
Two researchers say they have found a way to exploit weaknesses in the mobile telecom system to legally spy on people by figuring out the private cell phone number of anyone they want, tracking their whereabouts, and listening to their voice mail. — Independent security researcher Nick DePetrillo and Don Bailey, a security consultant with iSec Partners.
The Really Bad News...
"These attack scenarios are applicable to corporations and individual users alike," DePetrillo said. "Corporations specifically should start to take a look at their security policies for executives as this can impact a business very hard, with insider trading, tracking of executives, etc." (more)
The Really Really Bad News...
It doesn't look like the phone companies will (or can) fix this situation.