Great f**king idea
There is no way this will work.
Option 1: Make jammers a standard "feature" of automobiles. Queue the DIY instructions for disabling it. Or, better yet, watch in horror as enterprising individuals yank said jammers out of their cars to deploy them in less noble applications.
Option 2: Make it a "feature" of cell phones, implemented with the accelerometer/gyro/GPS/whatever. Circumvented in short time.
Option 3: Maybe the car has a built-in RF module which, when the phone picks up the signal, disables itself. That too shall be disabled and/or re-purposed to disable cell phones elsewhere.
Never mind that these ideas are ridiculous to begin with.