The external differences between the Apple iPhone 3G and 3GS are hard to discern with the naked eye. The major differences are internal and include processor speed and battery life.Know More
In terms of dimensions, the 3G and 3GS are the same size and thickness. Both have a 480x320 pixel resolution touchscreen that measures 3.5 inches on the diagonal. The 3GS weighs 4.8 ounces, compared to the 3G's 4.7 ounces.
Both phones offer Wi-Fi and Bluetooth connectivity.The battery life is slightly better on the 3GS in regards to Internet use and audio and video playback. The 3GS provides up to 5 hours of Internet use for 3G, 9 hours on Wi-Fi, up to 10 hour of video playback and up to 30 hours of audio. The 3G provides up to 6 hours of Wi-Fi use, 7 hours of video playback and 24 hours of audio playback.
The 3GS has a 3 megapixel camera with video recording, compared to the 3G's 2 megapixel camera that takes still pictures only.
The 3GS has a faster processor and more memory than the 3G, 600 MHz as compared to 412 MHz and 256 MB of RAM as compared to 128 MB.Other features included on the 3GS that are not present on the 3G include voice control, inline remote and a digital compass.