iphone 3gs upgrade to 4.1 preserving baseband

[hetrogeneous]

Hello,
I have a iphone 3gs firmware 3.1.3 factory settings,
I want to upgrade to 4.1 presering the baseband,
what version JB software I need to use redsnow,ultrasnow,pwnage tool and where can i find custom firmware.plz give the link.

[iYeow]

First thing is to find out if you have 4.1 shsh blob. If you have never jailbreak your iphone before, the chances is that you don't have 4.1 shsh blob.
Download tiny umbrella, plug your bootable iphone in and click save shsh.
If you only have 4.3.2 shsh blob, you are still safe.
Then in order to preserve your current unlockable baseband, you need to create a custom firmware from either Snowbreeze 2.6 or Pwnage tools 4.3.2
Download from iH8sn0w.com | Jailbreak your iPod touches and iPhones for Snowbreeze 2.6
Pwnage tools look at www.devteam.org or the latest news today.
Itunes must be the latest.
Use Redsn0w RC14 (not to jailbreak but to only put iphone into DFU mode) Pwnage tools DFU pwner.
Then run itunes : shift/Option + Restore and browse to custom firmware 4.3.2 you have just created on your desktop.
Make sure anything unclear, ask first before you do anything that might jeopardize your unlockable baseband.
Someone here will definitely be willing to help you out.