As promised, Dev Team has released Ultrasn0w 1.2.5 to unlock iOS 5.0.1 running iPhone 4, iPhone 3GS and 3G. Those users will older baseband can unlock their devices with Ultrasn0w 1.2.5, which is available on Cydia.
Yet, Ultasn0w does not support any new baseband version. To unlock your iPhone you should have a jailbroken device and the device should be working on one of the following basebands.
iPhone 4 : 01.59.00
iPhone 3G/3GS : 04.26.08 05.11.07 05.12.01 05.13.04 and 06.15.00
Currently, only the above basebands can be unlocked. To jailbreak iOS 5.0.1 on iPhone 4, 3GS or 3G you can use the latest Redsn0w 0.9.9b9 tool which is still tethered. iPhone 4S users need to wait some more time as the iOS 5.0.1 untethered jailbreak is being worked on by Pod2g. Once the jailbreak is released, ultrasn0w will also be updated to unlock iPhone 4S.