iPhone sets the bar when it comes to touchscreen phones.  The multitouch display is the most responsive on the market by a good margin, and it offers gesture-based controls like pinching, swiping, and double-tapping that combine with Apple's user interface to make for a really fun experience for the user.  iPhone's multimedia features and Web browser are second to none, and the forthcoming iPhone 3G will add high speed data and many new features to an already successful package.