Swap Iphone 4 and 3g for iphone 4s! +

I have a brand new iphone 4. Ive kept it with a screen protector and a case so its in perfect condition. Only got it last month. I also have a iphone 3G 8gb which works perfectly has a few scratches on the screen and back. Also has a very small crack coming from the base of the phone. Im after an iphone 4s. In good condition please. Can you please text me only as I might be at work.