At first glance, the iPhone 4 and iPhone 3GS may look very similar to each other. After all, they use the same operating system, run the same apps, and look like larger and smaller versions of each other. But are they really the same? What are the difference between the iPhone 4 and iPhone 3GS?

With a quick glance, the key differences between the iPhone 4 & iPhone 3GS are summarized below:

Well, for your interest, the detailed differences between the iPhone 4 and iPhone 3GS also have been listed below:

iPhone 4

The iPhone 4 uses an entirely new all stainless steel body design with sharper, more angular lines and a thin "metal band" that wraps around the sides of the phone. This metal band has integrated mobile and data antennas and is designed to improve reception compared to earlier iPhone models.

The iPhone 4 has a high-resolution 960x640 at 326 ppi 3.5", IPS, LED-backlit display with an 800:1 contrast ratio that Apple refers to as a "retina display."

The company uses this name because 326 pixels per inch (ppi) is said to exceed the 300 ppi that the human eye is able to differentiate individual pixels from twelve inches away. As a result, content on the display should look more like that in a printed book than on a computer screen.

The iPhone 4 has a chemically hardened "aluminosilcate" glass front over both the display and either a white or black frame and a chemically hardened white or black glass back as well.

iPhone 3GS

The iPhone 3GS uses a largely plastic design with a more prominent metal "lip" around the edge of the front and has a black or white plastic back. iPhone 3GS models with a white plastic back -- discontinued configurations with 16 GB or 32 GB of storage -- still have a black front, whereas white iPhone 4 models have both a white front and back.

The display on the iPhone 3GS also is 3.5 inches but is only 320x480 at 163 ppi with a 200:1 contrast ratio, noticeably lower resolution than the 960x640 at 326 ppi display on the iPhone 4. Both the iPhone 3GS and iPhone 4 have "oleophobic" oil repellent coatings on the front, but the iPhone 4 has the same coating on the glass back as well.

The audio visual capabilities of the iPhone 4 and iPhone 3GS are a major point of differentiation. The iPhone 4 has dual cameras -- a 5 megapixel HD video/still camera (720p at 30 FPS) with a "backside illuminated sensor," a 5X digital zoom, and an LED flash on the rear and a VGA quality video/still camera on the front designed for video conferencing over a Wi-Fi network with Apple's included "FaceTime" application. For now, unfortunately, "FaceTime" video conferencing only works between two iPhone 4 models. The iPhone 4 has dual noise-canceling microphones as well.

The iPhone 3GS, by comparison, has a single 3.0 megapixel camera with VGA video recording at 30 FPS and a single microphone. Both models have autofocus, macro, and white balance support, and "tap to focus" features although the iPhone 4 is reported to have a superior macro mode. The iPhone 3GS has basic "video editing" capabilities -- you can cut the beginning and end of a clip "in camera" -- but the iPhone 4 goes much further. When paired with a new iMovie application -- available for purchase separately for US$4.99 -- the iPhone 4 supports a variety of more full featured video editing and effects capabilities.

Internally, the iPhone 4 and iPhone 3GS models are considerably different as well. The iPhone 4 has an "Apple A4" processor of unspecified speed and 512 MB of RAM and the iPhone 3GS has an ARM Cortex A8 processor running at 600 MHz (downclocked from 800 MHz) and 256 MB of RAM.

Battery life has been increased on the iPhone 4 when compared to the iPhone 3GS too. Apple reports that audio playback has been increased to 40 hours from 30, talk time on 2G to 14 hours from 12, talk time on 3G to 7 hours from 5, Internet use on Wi-Fi to 10 hours from 9, amd internet use on 3G to 6 hours from 5. Each provides an estimated 10 hours of video playback and 300 hours of standby time.

Pricing in the United States for the iPhone 4 is the same as it was for the iPhone 3GS when it was released -- US$199 for the entry-level model and US$299 for the high-end model, offered with 16 GB and 32 GB of storage, respectively with a two-year AT&T contract. Both capacities are available in black or white for the same price. Note that this pricing is for "qualified" customers only. For "non-qualified" customers or those "who wish to buy iPhone as a gift," the price of these devices with a new two-year agreement is US$599 or US$699.

A newly introduced iPhone 3GS with 8 GB of storage in black only is available for US$99, again, for "qualified" customers with a two-year AT&T wireless contract.