i am going to share 100% solution tested by me to upgrade to 4.1 without having anything effect on the baseband
you can use it even the phone is on stuck on recovery loop or on apple logo after erasing all contents :

use the latest version of redsnow i.e. 0.9.6b2

download it from here:

http://xs1.iphwn.org/rs/redsn0w_win_0.9.6b2.zip

and download the stock original firmware 4.1 for the phone here:

Iphone 4G

Iphone 3GS

Iphone 3G


Step 1 ::

First you need to open Redsn0w 0.9.6b2 in Windows. The first screen will have you browse for your firmware file. You should navigate to the FACTORY firmware file that you downloaded. I don’t know why but they didn’t include the option to enter Pwned DFU mode on the first screen of Redsn0w so you have to select a factory firmware file to bypass this part of the process

Step 2::


After you have selected the factory firmware file that you downloaded, if you have an iPhone 3Gs it will ask you whether you have the old or new(patched) model. If you have the new(MC) model then select “YES” this is VERY important, if you have the new model and you select no you will have to restore with a factory 4.1 firmware file which will take away the possibility to jailbreak. (To identify if you have MC or Non MC model, go to Settings – General – About and scroll down to Model. If it’s MCXXXX then you have new (MC) model. If it’s something like MBXXXX, then you have old (non MC) model.)

Step 3::

Now click “next” and you will see Redsn0w apply kernel patches to the IPSW you selected.

Step 4::

On the next screen is where you’re gonna have a few different options. You may see more options than what are shown below, the important thing is that you want to select ONLY the option which is “Just enter pwned DFU mode right now” This option is basically doing what the DFU button in Pwnage Tool for Mac users does.

Step 5::

This is another CRUCIAL step, I cannot stress enough that you should ALWAYS read instructions carefully and make sure you are doing things right. Please power off your device while the device is plugged into the computer. DO NOT click “next” until your device is both powered off AND plugged into the computer.

Step 6::

This is a step we should all be quite familiar with, now we have to put the device into DFU mode. Just follow the on-screen instructions exactly how they are displayed and you will be fine.

Step 7::

If for whatever reason things get screwed up and you didn’t follow the instructions correctly you will see a screen like the one below. If that is the case please start over and read carefully, if you do not see a screen like the one below please continue to the next step!

Step 8::

Alright, we are nearly there! Congratulations on making it this far! We are but mere minutes away from having a jailbroken 4.1 device with the old(unlockable) baseband! After Redsn0w detects your device in DFU mode it will begin processing again and you will see it applying the Limera1n exploit to your device.

Step 9::

Alright, you are all set to restore your custom firmware! After you have applied the Limera1n exploit, you should see the screen below informing you that you should now be able to shift+restore in iTunes to restore with a custom firmware file. Click “Finish”

Step 10::

Now download the custom firmware for your phone and restore it
(using shift and restore)

Download the custom acitavted firmwares from here :

Iphone 4G

Part 1

Part 2

Part 3

Iphone 3GS

Part 1

Part 2

Iphone 3G

Part 1

Part 2

And you got the phone upgraded with the baseband intact

and all done