The iPhone Dev Team has released UltraSn0w 1.2.2 update to unlock iPhone 4, 3GS running over iOS 4.3.2 firmware.
UltraSn0w 1.2.2 supports iPhone 4 1.59.00, and iPhone 3GS with 04.26.08, 05.11..07, 05.12.01, 05.13.04 and 06.15.00 baseband.
UltraSn0w 1.2.2 does not support new basebands including 2.10.04, 3.10.01, and 4.10.01.
Note: iPhone 3GS users can upgrade their device to iPad baseband 06.15.00 which is unlockable but your device may lost GPS feature after the unlock process. Check: Upgrade iPhones 3GS to iPad Baseband
Requirement: Your iPhone with iOS 4.3.2 must be jailbroken to proceed for unlock, if that is not then follow our guides below to jailbreak iOS 4.3.2 first.
Unlock iPhone 4, 3GS over iOS 4.3.2 with UltraSn0w
Open Cydia and tap on Manage tab
Tap Sources > Edit > Add
Type this URL there http://repo666.ultrasn0w.com and tap Add Source button and let Cydia complete the process
Tap on Search tab and search for ultrasn0w and install it on your iDevice and the installation process will unlock your iPhone with the above supported basebands
Reboot your iPhone and that’s it
Enjoy, your iPhone 4, 3GS over iOS 4.3.2 is unlocked now and free to use SIM of any carrier of your choice.