Immersion is developing a type of touchscreen that will closely emulate real, mechanical buttons. So sum it up in a nutshell, you push on the touchscreen and it will push back with a small tap, throw a fancy click noise into the mix and it is practically like a real button. The system, called VibeTonz, can help all aspects of touchscreens use by utilizing other senses rather than just sight.
Immersion has been working on other tactile touchscreen technologies, likeTouchSense, that allows you to actually feel the buttons, scrollbars, etc. The VibeTonz "tapping back" technology sounds a little more useful for the mobile platform and maybe cheaper and easier to pull off on their part. VibeTonz can currently be found on the Samsung SCH-a930 from Verizon with more cellphones to come in the future.
Cell Phones to Get Tactile Touch Screens [Mobiledia]