Unlocking a Apple iPhone 4 will not work using an unlock code. However, any Apple iPhone 4 unlocked mobile phone should work on whichever phone networks or carrier you desire. The information below is only true for GSM or SIM card based version of the iPhone. (Update: If you have a CDMA version, you should check out this unlocking tool instead.)
Getting a free Apple iPhone 4 unlock code is possible, so I would first contact your phone carrier’s support line and request one. Sometimes they will give you one for free and in exchange will need your Apple iPhone 4′s IMEI number. You can get this number by typing *#06# on your iPhone keypad and then hitting enter. If you cannot attain a free Apple unlocking code, then you should review some of the unlock code websites I have provided below.
You should now be able to use your unlock code and the steps below to fully unlock your Apple iPhone 4 to other carriers.
How To Unlock iPhone 4G
1. Turn on your Apple iPhone 4 with an unaccepted SIM card.
2. The iPhone should now request the unlock code or request a password of some sort.
3. Now enter your unlock code.
4. Your Apple iPhone 4 may reboot and should now be completely unlocked.
Also keep in mind that if your Apple iPhone is not a GSM cell phone, then these instructions will not work. However, I am pretty sure that at the moment only GSM or SIM card based iPhones exist. Anyway, good luck unlocking the new Apple iPhone 4G and just leave a comment below if you need some additional help or tips.