New Samsung Galaxy S3 in White swap for new iPhone 4S in black -

I just got this on upgrade last week and its a little too large so I want to go back to an iPhone 4S. I am looking for a black iPhone 4S brand new with zero marks on and either unlocked or on O2. In return I have this lovely white sim free Samsung Galaxy S3 which is an unbelievably good phone. This will come boxed in its original box with everything that came with it intact (as it should be having only received it less than a week ago).