Can I "hide" the keyboard on my iPhone 4 the way you can on the iPad? When using my iPad to, for example, write an email, I have the option to press a button and hide the keyboard.  This is useful for reviewing an email prior to sending it.

Is there a similar feature with the iPhone?  If anything, this would seem particularly useful on the iPhone given its smaller screen.
Unfortunately not. I agree that this feature would be nice, especially since it's included on the iPad. The only way to review an email prior to sending it without having the keyboard on the screen is to save it as a draft, then reopen it. A little tedious, sure, but it might be worth it if it's a long email.