At&t is now allowing the unlocking out of contract iphones http://howto.cnet.com/8301-11310_39-57411361-285/how-to-unlock-an-at-t-iphone/

you do need to meet certain conditions though

as long as your gophone simcard is past its 6month use it will work in any at&t phone however att does not support the use of a gophone sim in an iphone they wont help you if they know you have it in a gophone and your data wont work either iphones use a differnt data network than the gophone setup has