iPhone Dev Team pushed out updated version of Ultrasn0w incrementing the version to 1.2.2 allowing software carrier unlock for iPhone 4, 3GS and 3G running iOS 4.3.2.

The new UltrasnOw 1.2.2 can unlock :

• iPhone 4 baseband 1.59.00 or lower.
• iPhone 3G/3GS baseband 4.26.08, 5.11.07, 5.12.01, 5.13.04 and 6.15.00

Here is the official update note from iPhone Dev Team:

“Note that there’s a corresponding update to ultrasn0w, which has been bumped up to v1.2.2 to get along with iOS 4.3.2 (the ultrasn0w update does not include any new baseband support!). Please reboot your iPhone using the normal “slide to power off” swipe after installing ultrasn0w 1.2.2.”