there is 3 kind unlock
1 . software unlock which is = dev team / gevey sim
2 . official unlock which is company unlock such as = ATT/APPLE
but official unlock when you restore your iphone it may need to reunlock again
which mean your phone become lock you have to get code unlock again
3 . never lock = this is unlock by manufactory , this free to upgrade version
your phone still unlock , you can restore do what ever you want still unlock all of times ...
i got 1 never lock version iphone 4
1 . software unlock is free but you have to wait so long , currently ios 5
not release yet
2 . official unlock $ 649/749/849 at
www.apple.com now
3 . never lock $ 849/999/1119 at
www.atgsm.com now