iPhone 4 16gb unlocked to all networks trade with samsung galaxy s2 unlocked, or 3 networ +

I would like to trade my iPhone 4 16gb black which has been unlocked to all networks by apple, with a samsung galaxy s2. The iPhone has a crack on the back of the handset but i will throw in a high quality bumper case which is very stylish. I actually prefer the phone with the bumper on. Just need to samsung to be unlocked to 3mobile or any network. Phone comes with charger and a charge dock which is very neat and allows you to plug headphones or speakers in. Please no sill offeres i just want a galaxy s2 or 250 so I can buy one myself. Thanks