You are responsible for everything that you do to your device. If you do any mistakes or mess something up it's your own fault. DO NOT BLAME ME or ANYONE ELSE.
I, Daily Mobile, iH8sn0w, nor anyone else takes any responsibility to any harm done to your equipment. You do this on your own risk.
This guide is made with sn0wbreeze 2.7.3, Windows 7 Ultimate x64 SP1, iTunes 10.2.1.1, iPhone 4 32GB locked to Telenor Sweden (MC605KS/A), baseband 1.59.00, and is based on my upgrade from iOS 4.2.1 to iOS 4.3.3.
------------------------------------------------------------------------
This is a guide for how to use this software. You should check that your version of iOS is jailbreakable. Always use the latest version of sn0wbreeze if you're not prompted to do otherwise.
------------------------------------------------------------------------
sn0wbreeze preserves your baseband
If you're running older, unlockable basebands (01.59.00, 04.26.08, 05.11.07, 05.12.01, 05.13.04 or 06.15.00), then you'll be able to continue to unlock using ultrasn0w.
If you have a newer, nonunlockable baseband, you're out of luck. Sorry, there is NO WAY for you to downgrade it.
You neediPhone
Windows compatible PC with Windows XP, Vista or 7 (32 or 64 bit)
.NET Framework 2.0
Data cable connected to an USB-port
on your computer do NOT use a hub in you keyboard, monitor or dedicated hub
iTunes
Download sn0wbreeze from
http://ih8sn0w.com/index.php/products/view/sn0wbreeze.snow and extract it
Download the IPSW for your device from
http://getios.com/Let's get started1. Open sn0wbreeze (d'oh).
2. Click OK, you did download it from them if you used my link, and then it was free!

3. Click the blue/white arrow down to the right

4. Now either brows for your IPSW or if you have it in an open folder just drag and drop it

Let it do it's thing

5. Select Expert mode (don't ask me why) and click the blue/white arrow

6. Select Build IPSW and click the blue/white arrow

Play PacMan! This will take some time depending on your computers performance

7. Now click OK to put your iDevice in DFU-mode.

8. Turn off your phone, connect it to your USB-cable and then click start.

Now follow the on-screen instructions, which are:
Press Home and Power button for 10 Sec.
Release Power Button while keep holding Home button for 15 Sec
sn0wbreeze will tell you that your iDevice is put in Pwned DFU-mode
9. Open iTunes and select your device in the left side bar.
10. SHIFT-click on Recovery. It will look somewhat different to this because I'm not in DFU-mode.

11. Open your custom IPSW from the desktop.
IT IS NOT THE FILE YOU DOWNLOADED!! It should be named sn0wbreeze_
iDevice Model-softwareversionIf you use the file you downloaded your baseband WILL BE UPDATED and you WONT BE JAILBREAKED. You will not be able to downgrade your baseband again!
SO BE CAREFUL
12. Go and grab a sandwich, a cup of coffee and chill. Let iTunes do it's thing.
Your iDevice will be rebooted and need to be activated when the update is completed.

13. When that's done, restore your backups if you want, or make it a new device for optimal performance.
14. Now install ultrasn0w from Cydia. Reboot. Done!
------------------------------------------------------------------------
You are responsible for everything that you've done to your device. If you done any mistakes or messed something up it's your own fault. DO NOT BLAME ME or ANYONE ELSE.
I, Daily Mobile, iH8sn0w, nor anyone else takes any responsibility to any harm done to your equipment. You've done this on your own risk.