Best upgrade scenario for 3Gs?

[jackryan57]

I have a 3Gs running 3.1.3 my baseband is 5.13.04 it is jailbroken.

I have lost track of all the jailbreak scenarios, I just can't keep up like I used to. I would like to upgrade to a 4.x version and jailbreak it. I would also like to keep a baseband that can be unlocked so when I get the iPhone 5 I can sell this one as an unlocked.

Can someone please tell me the steps involved and which ios I should upgrade to in order to have an untethered JB? You don't have to go into details on how to use each step in the jailbreak - just outline each step for me?

All my blobs are saved from 3.1.2 up to 4.2.1+

Very much appreciated

 

[machasm]

OK.
It looks like someone trying to do their homework before rushing in. Good news.

The 3Gs is a bit of a minefield but I'll try my best to explain.
The latest untethered JB will be IOS 4.1
You can safely upgrade to this using redsnow BUT do not update the baseband.
You will not be able to unlock the phone using ultrasnow, however, unless your 3Gs is of the old bootrom type. If it is, then use ultrasnow to unlock (If needed).
If you have a newer bootrom and still need an unlock then you will have to update to BB 6.15 (Which I would not recommend for the reasons you have quite clearly stated already).
I could be wrong here so please feel free to correct me all.
Mac.

 

[PsstGreek]

If you own a Mac or have access to one use PwnageTool. PwnageTool will safely upgrade your iPhone to whatever firmware you like and it will keep your current baseband.

 

[jackryan57]

If you own a Mac or have access to one use PwnageTool. PwnageTool will safely upgrade your iPhone to whatever firmware you like and it will keep your current baseband.

No mac, and I have the new boot rom

 

[Peppe]

I updated to 4.2 then downgraded to 4.1 and re-jailbroke from there using limeRa!n.
May not be the best way to do it but it worked for me.
Running baseband 05.15.04

Pep