An updated version of Ultrasn0w for iOS 5.0.1 has been released by the iPhone Dev team. Ultrasn0w 1.2.5 can now be installed on a jailbroken iPhone running iOS 5.01.
The user will still need an unlockable baseband to utilize ultrasn0w and if the user meets that requirement, it will be possible to unlock his iPhone 4 or iPhone 3GS running iOS 5.0.1.
The baseband must meet the following requirements:
iPhone 4: baseband 01.59.00
iPhone 3GS: basebands 04.26.08, 05.11.07, 05.12.01, 05.13.04, 06.15.00
The new version of Ultrasn0w is only for the iPhone 3GS and iPhone 4 and does not bring any new baseband compatibility, and currently there is no support for the iPhone 4S. However, it is expected that Ultrasn0w could support the 4S at some point in the future. UltraSn0w allows jailbreakers to unlock the iPhone for free to use on different carriers.
Also the only method for upgrading to iOS 5.0.1 while preserving the baseband that is compatible with Ultrasn0w is to use a custom IPSW created using Redsn0w. MuscleNerd, who is a jailbreak hacker, has advised users having iPhone 3GS with old bootrom to apply the latest Redsn0w 0.9.9b9d before installing the Ultrasn0w compatible update.