The iPhone Dev-Team has released UltraSn0w 1.2.7 to bring unlock support for some older basebands on iOS 5.1.1.
UltraSn0w 1.2.7 doesn’t bring any other new baseband support, only the following devices can be unlocked using this Cydia package:
iPhone 4 on baseband 01.59.00
iPhone 3G/3GS basebands 04.26.08, 05.11.07, 05.12.01, 05.13.04, and 06.15.00
Anyone who hasn’t updated to iOS 5.1.1 can now do so, as the latest version of UltraSn0w will software unlock your device. Unfortunately, no newer baseband support has been added and there probably won’t be.