yes
to get an iphone 3gs you can either buy it, find one, or win one anywhere in the world
It most certainly does. The only difference between 3G and 3GS is the processor speed and software. ALL accessories are interchangeable.
no why do you think its called trading in?
If you mean the difference it's quit alot. The iPhone 4 includes a retina screen, a new design and style, it shoots HD videos and pictures and it has flash. It almost the same as the iPhone 3GS...