The iphone-Dev team also notes that Blackra1n is not a carrier unlock method but only jailbreak tool. So, the iphone 3G and 3GS owners using ultrasn0w to for carrier unlock are advised to stay away. Updating iphone with 3.1 or 3.1.2 without using PwnageTool will bar the ability to unlock the device for quite a while.
Note that performing jailbreak and unlock voids the Apple Warranty on the respective device. This article is for informational purpose only and we aren't responsible if the device turns non-responsive. iphone
But updating to 3.12 with pwnage is fine. UltraSn0w is working on 3.12 with BB preserved at 04.26.08 and my phone feels 'snappier'
pkgbackup has also worked without a hitch (unlike the 3.1 update)