If you are an iPhone detractor due to its lack of a physical keyboard, 4iConcepts has a product for you. 4iThumbs 2 is a screen protector that adds tactile functionality for users looking to feel what they're typing.
I received a test unit last week from 4iConcepts and, as they state, the screen protector adds a BlackBerry-esque keyboard feel to your iPhone 4. Simply apply the plastic screen to your iPhone in the proper direction and next time you pop the virtual keyboard, little bumps will be on each key.
Though the cover has the bumps, pressing any icons, playing games, and otherwise operating your iPhone still works just fine, if not a little odd.
You have the choice of purchasing a landscape or portrait-oriented keyboard (or both, of course). 4iThumbs 2 for iPhone 4 will run you $19.99 (for both) from the 4iConcepts Web site.
Tactile feedback was never much of a concern for me, so continued use of the 4iThumbs 2 screen protector is unlikely, but if you're looking for a solution to the lack of a physical keyboard and don't want to carry an external Bluetooth keyboard with you, 4iThumbs 2 is a nice way to go.