Features

Touch screen

The 3.5 in liquid crystal display (320×480 px at 160 ppi) HVGA touch screen topped with optical-quality glass is specifically created for use with a finger, or multiple fingers for multi-touch sensing. Because the screen is a capacitive touch screen, no stylus is needed, nor can one be used. The requirement for bare skin to be used has caused concerns for users in areas with winter climates; gloves worn would then have to be removed to use the touchpad.
For text input, the device implements a virtual keyboard on the touchscreen. It has automatic spell checking, predictive word capabilities, and a dynamic dictionary that learns new words. The predictive word capabilities have been integrated with the dynamic virtual keyboard so that users will not have to be extremely accurate when typing — i.e. touching the edges of the desired letter or nearby letters on the keyboard will be predictively corrected when possible. The keys are somewhat larger and spaced further apart when in landscape mode (currently, only using Safari). Reviewers, writers and analysts have pointed out several areas in which the iPhone falls short. The virtual keyboard has been considered its chief weakness and a risk for Apple.David Pogue of The New York Times and Walt Mossberg of The Wall Street Journal both tested the iPhone for two weeks and found learning to use it initially difficult, although eventually usable. Pogue stated use was "frustrating" and "text entry is not the iPhone’s strong suit" but Mossberg considered the keyboard a "nonissue." Both found that the typo-correcting feature of the iPhone was the key to using the virtual keyboard successfully.
The iPhone varies from common desktop interfaces by using a direct manipulation model of scrolling. Where a typical desktop GUI achieves scrolling by using a scroll-arrow to push a view-window down and thus the content itself up (or the reverse, clicking up to move content down), the iPhone interface enables the user to move the content itself up or down by a touch-drag-lift motion of the finger, much as one would slide a playing card across a table. Additionally, the speed desired for scrolling is computed based on the speed and acceleration with which the drag motion is performed.
Scrolling through a long list works as if the list is pasted on the surface of a wheel: the wheel can be "spun" by sliding a finger over the display. After the finger is lifted from the display the wheel continues to "spin" for a short moment before coasting down. In this way, the iPhone seems to simulate the physics of a real object, which, it is thought, should give a natural feel to the whole process.
The user interface also features other visual effects, such as horizontally sliding sub-selections and co-selections from right and left, vertically sliding system menus from the bottom (e.g. favorites, keyboard), and menus and widgets that turn around to allow settings to be configured on their back sides.
The photo album and web page magnifications are examples of multi-touch sensing. It is possible to zoom in and out of objects such as web pages and photos by respectively "unpinching" and "pinching" them, that is, placing two fingers (usually thumb and forefinger) on the screen and moving them farther apart or closer together as if stretching or squeezing the image. This scaling is done uniformly and proportionally based on the image in question so there is no distortion of the image itself, as would be the case if the image were actually stretched or squeezed.
One disadvantage of multi-touch with regards to AJAX web sites is that there is no mechanism for 'hovering' over a UI element. That is, there is no separate paradigm for indicating interest or focus on a portion of a web control other than clicking on it.