“If there is a billion-dollar gamble underlying Apple’s iPhone, it lies in what this smart cellphone does not have: a mechanical keyboard. As the clearest expression yet of the Apple chief executive’s spartan design aesthetic, the iPhone sports only one mechanical button, to return a user to the home screen. It echoes Steven P. Jobs’s decree two decades ago that a computer mouse should have a single button. (Most computer mice these days have two.) His argument was that one button ensured that it would be impossible to push the wrong button.”
Link: That iPhone Is Missing a Keyboard (nytimes.com)


It should be possible for the iPhone to give some feedback through the vabrate motor.
http://yandleblog.com/2007/03/will-iphone-feature-haptic-feedback.html
You’re absolutely right. Unless Jobs has something up his sleeve, I think that the lack of keyboard feedback will be the real limitation on the iPhone’s success.
http://blog.wouldbetheologian.com/2007/06/real-problem-with-iphone-no-haptics.html
The Real Problem with the iPhone: No Haptics…
Im holding off on the iPhone. Sure, its spendy, but not having seen the real thing yet I suspect the real problem will be the keyboard. On my Cingular 8525, about the only thing I use the touch screen for is dialing numbers not already in m…
Since most people won’t write novels on the iPhone, I think the visual feedback on the screen is completely sufficient…
So here’s my issue with touchscreen handsets (and this also extends partly to QWERTY): it’s really hard to walk down the street and write an SMS using just one hand. You’ve got to look at the screen to target which is something I don’t need to do writing T9 predictive text; I can effectively touch type in T9. It can also be much harder to target generally without raised buttons. Touchscreen phones are a step backwards for me in this regard.
(I’ll admit I’m not an American, and Americans typically don’t use predictive text like people in most other countries).