I have an unlocked and jailbroken 3g that is on 3.1.3. I want to update to 4.1.2. Can I stay unlocked AND untethered on this phone? I'm confused with all the different tutorials out there.

I know this has an older baseband on it now. I want to keep that, right? Since this is my son's phone, I can't have a tethered unlock/JB.

Please point me to the correct tutorial or walk me through the steps.