Looking for Iphone 3GS part exhange for Blackberry 8520 Curve ?

Looking for an Iphone 3GS must be unlocked and working. Must be in good condition, must come with charger will part exchange for my Blackberry 8520 Curve. Comes with box and accessories, cover, chargers - socket, in car and usb cable. Will pay cash in part exchange for Iphone but please make the offer sensible. IE not full price of the Iphone and expect the Blackberry Free of Charge! Email if your phone meets the above criteria 8gb considered preference for 16gb