Selling Iphone 4 and Iphone 3 - Swap ?

Hi, I would like to swap my white Iphone 4 16GB, its good condition and has been looked after. it comes with original accessories and also 3 cases. i would like to swap it please email me with your offers. i also have a iphone 3 which i would also like to swap. No blackberrys for iphone 4 but will swap for iphone 3. Thanks.