Yes
The new iPhone 4 does.
no
iphone 3g don't but 4g and 5g have flash iphone da abn a7ba
HD screen, Face time, flash camera, HD camera, wider sceen, longer battery life...ECT
iPhone can call has messenger camera flash and a slightly higher resolution and camera resolution
It is definitely faster, it has a front facing camera for video conferencing, the back facing camera has a flash, and it has a higher resolution screen.
Microphone
iPhone 4: 5MP 720p HD Camera iPhone 3GS & Below: 3MP Camera
iPhone 4 has a range of improvements including high resolution screen, gyroscope, improved processor, 512MB RAM, 5 megapixel camera with flash and a front facing camera for video calling. ----------- iPhone 4 has better specs than 3gs. You can check some reviews on this site. (See the sources below)
The iphone 5 has an improved 8 megapixel camera.
Yes, you can put an iPhone camera in an iPhone 3GS provided you have the required skills.
Yes, all iPhone's have a rear camera, however, only the iPhone 4 and 4S have a front facing camera as well.