I unlocked with ultrasn0w but after unlocking a friend's phone with black0snow i'd rather use that. Can I restore and upgrade to 3.1.2 and then unlock with blacksn0w? If not, can I upgrade to 3.1.2 via quickpwn and remain unlocked?
your choice is to either stay on 04.26 and upgrade with a patched 3.1.2 firmware from pwnagetool (mac only), or you can update to factory 3.1.2 from apple (which will update your base band to 05.11.07) and then run blackrain/blacksnow from windows (or jailbreak with pwnagetool + blacksnow).
If you have access to a mac i would suggest doing the first just to keep the 04.26 baseband (i'm paranoid that way), but if you only have access to windows you can do the second way.
It isn't wrong to be safe and stay on the 4.26.xx baseband but it's a hassle to try and preserve the baseband when the new one is fully unlockable. The easiest way is to update to 3.1.2, jailbreak with blackra1n, then unlock with blacksn0w. But if you truly want to stay on the old baseband, you'd have to preserve the baseband by either finding and downloading a custom firmware or if you have a mac make your own. But honestly it's just so much easier to click upgrade then do all that searching.
My 3G I didn't bother updating until they released the new unlock cuz honestly I just didn't feel like spending the time to do everything perfect.