iphone 4

any iphone 4 which bought from the operator in Hong Kong or ordered it from Apple Online Store(HK) is not sim locked, it means u can use any SIM card among the word.
But now, Apple online store (HK) have stopped any ordering since a long time ago, u cannot order it anymore. So if u buy iphone 4 in 百老匯 or 豐澤, you should pay more, and it could be used in US wihout doubt.

so, if u bought ur iphone4 in US (via AT&T), those iphone have been modified that could be used with AT&T sim card but not for other, and it cannot be unlocked nowaday, maybe temporaray.

2011-01-23 18:03:19 補充：
係香港上台出既 iphone 4

或係 apple online store (hk)

豐澤, 百老匯等買既行貨

都唔會有 sim lock，去到邊都用得到，唔使解

但宜家
apple online store (hk) 已經暫停 order，無得訂
去 百老匯 or 豐澤 買都得架，如果佢地有貨，而你又肯俾多 d 錢的話

如果你係美國出 iphone 4 就一定有 sim lock，只可以用到 AT&T 既 sim card，咁就宜家暫時無得解

你係香港買嘅行貨,全部都冇 sim lock,去到邊都用得!