Description

Design
One of the most obvious differences between the iPhone 4 and past models is the new look of the phone. For one, it's noticeably thinner: the iPhone 4 measures just 9.3 millimeters thick -- 24 percent thinner than the already-svelte iPhone 3GS. Apple says it is "the thinnest smartphone on the planet."
The iPhone 4 also is more squared-off in shape, with a thicker metallic border running around the phone's edges. The new phone doesn't feature the plastic backing found on the iPhone 3GS and the iPhone 3G. Instead, the front and the back of the iPhone 4 are covered in aluminosilicate glass, which Apple says is found on helicopter and high-speed train windshields. It's designed to be significantly stiffer (20 times) and harder (30 times) than plastic, with a fingerprint-resistant finish.
Display
One of the iPhone 4's most-hyped features is its new display, which features an astounding resolution of 960 by 640. It measures the same size as the screen on the iPhone 3GS (3.5-inches diagonally), but packs in four times as many pixels. Apple calls it a "Retina display," and says it offers more pixels than the human eye can see. Experts have already begun debating that claim, but the iPhone 4's screen should still look remarkably crisp and clear.
Software
The iPhone 4 will run version 4, the latest version, of Apple's iPhone OS, which has been renamed: it's now just iOS. iOS version 4 adds several new features, including a long-desired multitasking capability, which will allow you to run more than one third-party app at a time. Other new features in the new OS include folders for organizing all of your apps, a new Mail client, and a Game Center.
Browsing the Web
Despite the "4" in its name, the iPhone 4 does not support 4G wireless networks. Still, you do have plenty of options for speedy Web browsing. For one, the iPhone 4 now supports 802.11n wireless networks, which are faster than 802.11b or g networks. And you still get support for AT&T's high-speed 3G network.
Camera
The iPhone 4 features not one but two cameras: a forward-facing camera for video chat and a rear-facing camera for capturing photos and videos.
The rear camera is a 5-megapixel shooter, which should be a big step up from the 3.2-megapixel camera found on the iPhone 3GS. It adds an LED flash and a 5x digital zoom.
In addition to snapping photos, the camera can record HD video clips at a resolution of up to 720p. Apple also will release an iPhone-compatible version of its iMovie video editing app to coincide with the release of the new iPhone.
FaceTime
iPhone users have long wished for video chat capabilities, and with the iPhone 4, they get their wish. The phone's front-facing camera will allow for use of a feature called FaceTime, which allows users to make video calls. While the capability sounds impressive, it does come with some serious limitations: it works from iPhone 4 to iPhone 4 only, and video calls can only be conducted over Wi-Fi networks.
Additional Features
The iPhone 4 will feature Apple's own A4 processor and a bigger battery; Apple says the chip has power-saving features that, combined with the bigger battery, will deliver 40 percent more talk time.
The new iPhone also features a gyroscope, which, in combination with the phone's accelerometer, will deliver more specific motion detection.

Source : www.cellphones.about.com