If by this you mean what is new about the new operating system, you can create folders, use multiple apps at a time, video chat with FaceTime and Skype, stream music from your Mac or PC, use your iPhone as a personal WiFi hotspot, and much more. (link below
What you do is you go and plug up ur iPhone to the iTunes and click on the update button
Yes the iphone 4 is better so you should upgrade to the iphone 4.
with the new 3.0 software update it is expected to be possible
iOS 4 was released long ago back in 2010 along with the iPhone 4 and was a free update. It could be downloaded on any device except the original iPhone and 1st generation iPod Touch.
Simply update ios
it will not update and if it does it might lock your phone and you will not be able to use it.
one of the main things in the new iPhone is it has a flash camera with auto touch focus. you touch the part of the picture you want your camera to focus on. The iPhone 4 is also 24% than the iPhone 3gs/3g. but there is an update for the older iphones for the new features. The display on the new iPhone is so good that the human couldn't possibly so the amount of pixels.
it gives you air play and makes it harder to jailbreak
depends if it has 4.os update
Yes, if you update it to iOS 5.1.1, there is an untethered jailbreak out.
plug your iphone into your computer and go into itunes click on your phone under devices go to summary and press check for update or update iphone.
Yes. If you update your iPhone's software using iTunes it will lock your iPhone again. You will then need to unlock it again.