Finally, I decided to upgrade my iPhone OS from 4.2.1 to 4.3.3. All thanks to Dev-Team members and Sn0wbreeze to make possible the installation, untethered jailbreak using Greenp0ison. And of course to @MuscleNerd for Ultrasn0w unlock update.
I used Redsn0w to change my iPhone baseband to iPad baseband 6.15.00 so that I could use Ultrasn0w to unlock iOS 4.1 which was the most difficult version to breakthrough that time & process was little difficult as well. Later, I wanted to preserve this baseband of 6.15.00 on my iPhone (Remember: This is not the usual iPhone baseband at all.) when I wanted to upgrade to 4.2.1 which was successful at the end by using Sn0wbreeze.
Similarly, I selected Sn0wbreeze (A Custom IPSW Creator for 4.2.8/4.3.3) because I found it easy to use on Windows. This is a long post with lots of images to give clearer view of the process.
Please ask before proceeding if you’re unsure
I am writing a step-by-step guide here to Install, Jailbreak and unlock iPhone 4.3.3. You may choose to jailbreak iPod Touch, iPad with the same method except leaving the options that are only available to locked iPhones. You should jailbreak factory unlocked iPhone with Redsn0w
UPDATE: Before you begin
The newer version of iTunes (after 10.2.2) is not allowing people to install 4.3.3 because there are higher version of iOS now available. This is irrespective of whether you have changed 3GS baseband to 06.15 or not for ultrasn0w unlock.
You would need to uninstall iTunes 10.4 or later and clean install iTunes 10.2.2 to be able to install custom 4.3.3 IPSW and get rid of 3194 error.
Also make sure your ‘hosts’ file has the following
74.208.10.249 gs.apple.com 127.0.0.1 localhost
Download iTunes 10.2.2 here (77.13 MB)
It will NOT WORK if
You have 3GS which is built after 35th week of 2011 and if iPhone’s serial number starts with xx135
Step 1: Collecting essentials
1.1] Select and Download required 4.3.3 OS stock firmware file from this download page OR new source here . [If you're on iPhone 3GS then you should choose 'iPhone 3G S (4.3.3/8J2)']
1.2] Download & install Sn0wbreeze 2.7 from this page
* Sn0wbreeze requires .NET Framework installed on Windows computer. Click here to download if you do not already have it.
1.3] Download and install iTunes 10.2.2 (This is a must because it supports 4.3.3)
1.4] Take backup of iPhone data with iTunes.
1.5] If you have a jailbroken phone & Cydia apps installed on it then use AptBackup package from Cydia to backup application list.
Step 2: Open Sn0wbreeze
We can (and must) create a custom jailbroken firmware for the specific device from the IPSW file we downloaded from above step. This is an essential process and made simple by Sn0wbreeze.
Click ‘OK‘ and then click on blue button until it shows you Sn0wbreeze version & welcome message.
Step 3: Provide IPSW to Sn0wbreeze
In this step, we are going to feed Sn0wbreeze with the stock IPSW we downloaded above. Click ‘Browse’ to locate and select the IPSW file. In this process, Sn0wbreeze will validate the selected IPSW and detect the device it is meant for.
Step 4: Confirm detected IPSW & Bootrom
Once IPSW is scanned, it will show you the device and will prompt to select bootrom version. Just select “New-Bootrom/Don’t know” and click next to continue.
Step 5: Preparing custom IPSW and settings
Here, we are going to configure the custom firmware or custom IPSW which we’re going to use on our phone. There are few settings needs to be checked here. Sn0wbreeze will prompt to choose 3 modes to continue. Details of each mode can be read by hovering the mouse on these options. We’re going to select “Expert Mode” (Aren’t we experts already? 
) and click continue.
Now, on the next screen we will see few options like, General, Unlocks, Custom Boot Logos, Custom Package and Build IPSW. Each of these menus have different settings to choose but we are only going to use “General”. Select it and click continue.
Now, we are on “General” settings page. See the image and check those options. We do not need SSH & battery percentage. Also keep the default values for the root partition size. Click continue.
Next screen will show a list of Cydia repositories. Skip this to avoid any confusion. We can always do it later. Then another screen will prompt for an option of installing iPad baseband 06.15.00 for iPhone 3GS. This is important if you want to unlock 3GS with Ultrasn0w and you’re on 05.14.02 firmware with 06.02 bootrom or higher.
If you’re already on 06.15.00 or older bootroms then ignore this and click continue.(If you’re unsure or getting confused with this step then reply to this post & I will reply back)
Step 6: Baking custom IPSW
Continued from earlier step – Sn0wbreeze will now create a custom IPSW for us. Wait until it finishes creating it. Once completed it will show us the “Done” screen.
Step 7: Put iPhone in DFU mode
To install custom firmware on iPhone, we must put it in DFU mode first. This step if could not be achieved then re-do it by disconnecting the cable and putting back again & repeat the process mentioned here. These will be shown on Sn0wbreeze screen as well.
1] Power Off iPhone
2] Press Home + Power button together for 5 seconds (watch for on-screen countdown)
3] Release Power button and keep holding the Home button until you see “Found New Hardware” [DFU mode] prompt. See image below.
4] It will show you once the iPhone is successfully enters in to DFU mode. Click “Okay” & then exit Sn0wbreeze,
Step 8: Almost there
Open iTunes while iPhone is still connected. Click OK to “iTunes has detected an iPhone in a recovery mode. You must restore….”
We need to install custom firmware on iPhone which we just cooked in earlier steps. Click SHIFT + RESTORE to select our custom firmware. Sn0wbreeze – by default – saves custom cooked firmware on Windows desktop.
Step 9: Be patient
Wait patiently while iTunes validates installing (restoring) new firmware on iPhone. It will prompt and restart iPhone to complete. We should see Sn0wbreeze logo on iPhone while it installs our custom firmware.
Step 10: Done. Restore iPhone backup
Now, iPhone is ready with new OS version 4.3.3 on it. All we have to do is, restore iPhone backup we created before Step 2 above. iTunes should take about 20 mins to finish restoring data.
We’re done.
Step 11: Unlock iPhone
We have Cydia installed on our new iPhone 4.3.3 with default repositories including Ultrasn0w (repo666.ultrasn0w.com). Install Ultrasn0w 1.2.3 to unlock iPhone.
Video
This is a quick, basic video I have just for a quick reference. (I need to work a lot on video)
Voila!!
If these steps are confusing then please feel free to buzz me via comments below. Also let me know if it worked for you.
(This guide is for illustration purpose only. Do not use this guide if you’re unsure about what you’re doing. Updating modem firmware will void any warranties on your phone)
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