Where can i trade my samsung galaxy s2 for the samsung galaxy s3 ?

Sony Ericsson Xperia X8 simfree phone
The Sony Ericsson X8 is an entry-level Android smartphone, rather like the X10 Mini, but with a larger screen able to handle a broader range of apps. it comes with charger,2gb mirco sd card and spare back cover. the case as wear and tear but screen good due to protector.