Do you want to update your iPhone 3G/3GS/4 to iOS version 4.1, jailbreak, unlock, and use it on T-Mobile? If you have baseband 05.13.04 on your iPhone or iPod and have iTunes 10 or later, you can by using Sn0wbreeze..
Here are the steps to take if you want to jailbreak, and unlock your iPhone 3G/3GS/4 on 4.1. I will say that you do this at your own risk, and I cannot be held responsible for any damage caused to your phone, if you do this incorrectly. Make sure you have the latest version of iTunes installed too.
Download Sn0wbreeze 2.1 from this link http://hotfile.com/dl/82255880/cd8eacf/sn0wbreeze-2.1.zip.html. Sn0wbreeze is made by iH8snow http://ih8sn0w.com/index.php/welcome.snow
Download the iOS Firmware
Download iOS 4.1 Firmware for your device from this link http://www.iphoneheat.com/2010/09/download-ios-4-1-firmware-for-iphone-and-ipod-touch/
Start Sn0wbreeze and follow the instructions on the computer screen, and select the firmware that you downloaded. Select expert mode. On the next screen select General, then hit the arrow. If you are not using the official carrier make sure that the “Activate the Iphone”(hacktivate) option is selected. Click the arrows until you get back to the main screen.
Build the Custom Firmware
Click Build ISPW. Let Sn0wbreeze work its magic. It will create a custom firmware for your iPhone or iPod. The great thing about this is that, Sn0wbreeze will not update your current baseband! Once it has finished it will place the file on the desktop.
Follow the Instructions
Sn0wbreeze will prompt you to connect your phone and turn it off. It will then tell you and show you how to put your iPhone or iPod into DFU mode. Follow the instructions exactly, do not deviate from them, if you want to successfully jailbreak and unlock.
Once the Iphone has been placed into DFU mode, iTunes will start and will say the device connected needs to be restored. Hold the shift key and click restore. Select the custom firmware file that Sn0wbreeze created. Make sure you select the correct file. The file name will start with Sn0wbreeze. Sit back and let iTunes do its thing
Unlock with Ultrasn0w and Cydia
Your phone will reboot and you will have the custom 4.1 firmware on your phone. Now if you want to Unlock to use on T-Mobile. Join a Wireless network and open Cydia, it will prompt for an update, go ahead and update. Once done, go back to Cydia and then search for Ultrasn0w. Install Ultrasn0w, once done you will need to restart your iPhone, and then it will be unlocked.
That’s it, your phone is now jailbroken and unlocked. Remember, I cannot be held responsible for anything that may go wrong. Follow the steps exactly and you will be jailbroken and unlocked.