If you're looking to preserve your iPhone's baseband when upgrading to iOS 5 on a Windows machine, then Sn0wBreeze is your ticket to baseband freedom.
Preserving your unlockable baseband is integral to being able to unlock your phone when an updated version of UltraSn0w is released tomorrow.
Windows users, this one's for you. Check inside for the full video tutorial that shows how to preserve your baseband, while upgrading to iOS 5 using Windows...