cell phone vibration mechanism?

I'm serious about this.......It occurred to me that the device used to make your cell phone vibrate is far superior to the mechanism used in many "adult toys" they are smaller and more powerful. In the interest of building a better "mouse trap" so to speak, I wonder if anyone has incorporated into a better designed toy? Perhaps a slide control for vibration level and a rechargeable battery circuit. In my research I've seen devices that can be triggered remotely via cell phone, but I'm thinking more along the line of a pocket pal. The old style used a spinning weight variable in speed that would create the vibration by off balance. How do these new ones in the phones work?