It's not possible. This nonsense comes up about every 2-3 months. IT CAN'T BE DONE. Common sense should tell anyone with half a brain that there's a frequency difference, lack of hardware, and a software issue. It's like asking if my can opener can be used to control the TV like a regular remote.
Apps like Trapster
are simply publicly accessible maps that show recorded locations of speed traps, as reported by other users. If you have GPS you can use it to tell you when you're nearing one of the pre-recorded speed trap sites and have your phone give you an audible warning. It's simply waypoints on a map being monitored by your GPS. Cool, but hardly revolutionary. But please, don't expect your phone to detect the police radar trap from the radar emissions of the radar gun.