all those whose iPhone 4, 3Gs needs to be unlocked there here is a solution for you..
Ultrasn0w 1.2.3 has been released to make unlock for iOS 4.3.3 on iPhone 4, 3GS running on Old basebands.
It should be noted though that this release of Ultrasn0w is not a new unlock for iPhones with newer basebands, instead, it only fixes the compatibility issues on the existing devices, which are jailbroken (with preserved basebands: 01.59.00 / 04.26.08 / 05.11.07 / 05.12.01 / 05.13.04 / 06.15.00) on iOS 4.3.3.
For iPhone 3GS
you need to upgrade iPhone baseband 3GS to 06.15.00 for unlock.
Click here to know the complete details for upgrading to the specified baseband.
NOTE- updating to 06.15.00 (iPad's baseband) might result in loss of GPS functionality.
Step 1- first jailbreak your iphone 4, 3Gs on iOS 4.3.3 and preserve the baseband using pwnage tool on mac or sn0wbreeze on windows.
Step 2- once you are done, then you can unlock the iPhone on the supported basebands using ultrasn0w 1.2.3 from cydia.
to do this
1-start CYDIA on your iPhone
2-touch on the MANAGE tab on the bottom
3-Now touch on the SOURCES
4-Now tap on EDIT and then tap on ADD. you will be prompted to add an URL source. type http://repo666.ultrasn0w.com and tap on ADD SOURCE to add this repo.
5-after installation is complete search for ultrasn0w 1.2.3 and install this application.
Now simply restart your phone and VOILA you are freeeeeeee.......