iPhone 5 black 16gb swap galaxy s3 -

i want to swap my black iphone 5 16 gb for a galaxy s3 , my dad bought me a iPhone when they came out as a early christmas prezzie , he got it from the vodafone shop so it could be locked to vodafone im not sure ? its had front and back screen protectors from new and been in a case and is only 2 week old but i want a galaxy s3 it must be sim free and pay and go, and must be like new condition i can travel local i.e. teesside will sell for £400 comes as new