How much does it cost to upgrade to an iPhone 3GS on an O2-UK iPhone tariff?

that is the sad part about iphones. you still have to pay full price for the phone even if you have an upgrade or not. here , iphone3G is 99$ plus tax or tariff. and iphone 3GS is 199$ plus tax or tariff. (i would reccommend getting an otterbox for a phone like that , they are the best way to protect your phone and even keep it from getting wet. (: hope i helped,