This week the Dev Team released redsn0w 0.9.10 beta 6 which does tethered jailbreak on iOS 5.1 to a multitude of iDevices, except iPad 2 and iPhone 4S. In the documentation published for this update, the Dev Team mentioned the fact that ultrasn0w is not yet compatible with iOS 5.1, but that an update will be released in the next period. Well, a few good days have passed since then and the update has not been released, but a developer published in a Cydia repo a package called ultrasn0w fixer that allows users to install and use ultrasn0w on iOS 5.1.
I haven't checked the package and I don't know if it works 100% correctly, so switching to iOS 5.1 and using ultrasn0w fixer is at your own risk. To switch to iOS 5.1 and keep the baseband intact you can make a custom ipsw with redsn0w 0.9.10 beta 6 or sn0wbreeze 2.9.2 but if you don't have SHSHs for iOS 5/5.0.1 you won't be able to go back to those versions of iOS. After installing iOS 5.1 add the repo: http://repo.iparelhos.com In Cydia, install ultrasn0w fixer from it then install ultrasn0w from the Dev Team repo, which is automatically added to Cydia, and reset the device and on reboot it should be decoded.
The basebands decoded by ultrasn0w are the old ones, i.e. maximum: 01.59.x, 05.13.x, 06.15.00.
Thanks to M.
