With an Unlocked and Tethered Jailbroken iPhone 3GS, will the UNLOCK remain in effect when rebooted without being connected to a computer?

I realize the jailbreak will need to be restored, but that is not a big deal. I'm more interested in having the phone remain unlocked.

Don't think you understand -- when the phone hard reboots on a 3GS with the new bootrom that has been jailbroken, it sits at the emergency screen until you kickstart it. It's not usable as a phone until it has been kickstarted. So, while the unlock may be valid, the phone is emergency call only until you kickstart. It's not that the phone boots into an un-jailbroken firmware, it's that the phone itself won't boot.

Hope this answers for you!

Which 3GS firmware/iphone serial numbers allow an un-tethered jailbreak?

You can use the following tutorial for kickstarting.
Gadgets and You: Fix for DFU or Recovery mode problem after unlocking iphone 3GS on 3.1.2 with redsn0w or blackra1n

Originally Posted by arw

Which 3GS firmware/iphone serial numbers allow an un-tethered jailbreak?

Week 40-45 of the iPhone 3GS is about when the new iBoot was implemented which is not exploitable for an untethered jailbreak. Anything before there can be assumed to have the old iBoot, anything newer can be assumed to have the new one. Ultimately, this is an educated guess. It is wholly recommended that you plug the device in to your computer and properly pull the iBoot revision as documented in several other posts on the forum -- you don't want to be incorrect about which version you have if you're asked.