i'll break it down for u ya..
unless u r planning 2 migrate 2 usa, it is not advisable to get an iphone frm usa or any locked set..
it cud be cheap..but u wud hv 2 compromise on lots of tings...
my advice, go 2 usa, hv fun..enjoy ur holiday, n get it frm spore or frm certain ppl in gs

i hv a feeling is hardware unlock
sm sellers try 2 act smart n say, "boss, dun wurry, fully unlock confirm working with 3g..."
no need turbo sim bla bla
but in the end they try 2 pwn it with winpwn or smting n gv stupid reason
1st hand experience