As expected earlier today, the Dev team released an unlock for iPhone 4, 3GS devices running 01.59.00, 04.26.08, 05.11.07, 05.12.01, 05.13.04, and 06.15.00 basebands.
If your baseband is different from any of these, there is no unlock available at this time.
Its already confirmed in the past that there will be no iOS updates, unlocks, jailbreaks for iPhone 3G and iPod touch 2G models.
Tutorial for iPhone 4 Windows users only:
Lets break the tutorial into three parts – Preserve baseband, Jailbreak, Unlock
Step 1: First, you will have to jailbreak your device using TinyUmbrella on iOS 4.3.1 and preserve the baseband mentioned above [Settings > General > About > Modem Firmware].
Step 2: Download TinyUmbrella from here [v4.30.05, 1.7MB]
Step 3: Connect your iPhone 4 and launch TinyUmbrella. Click ‘Save SHSH’ button (make sure SHSH were saved, if not don’t bother continuing)
Step 4: Click ‘TSS Server’ button (If you get errors, consult Google to fix it instantly, typically it fails because you have some kind of web sharing enabled. Use the comments section for delayed help)
Step 5: While TSS server running, launch iTunes
Step 6: Now, in iTunes, click Restore. Do not click Update.
Step 7: During the restoration process, iTunes should give error code 1013. Nothing to worry. This error means your baseband has been preserved. Now, exit iTunes
Step 8: Now, turn your iPhone into DFU mode (Hold Power button and Home button for 10s, release the Power button, and continue holding Home button for another 5s. If your timing is even a little bit off, you will see the Apple logo and your phone will boot back into recovery mode. Go back to step 8 and try again!)
Step 9: In the DFU mode, click ‘Fix Recovery’ and ‘Yes’ to proceed further.
Step 10: Your device’s screen will turn white and you’ll see debug boot information. Your iPhone 4 will now be on 4.3.1 with the preserved baseband.
Step 11: Now, to jailbreak your iPhone 4 on iOS 4.3.1, download RedSn0w from here [v0.9.6rc12]
Step 13: Launch RedSn0w and select the firmware you downloaded in the above step.
Step 14: While RedSn0w prepares to jailbreak, in the next step, choose ‘Install Cydia’ and click next
Step 15: Follow the on screen instructions to enter into DFU mode, once completed, you should see a pineapple!
Step 16: Your iPhone will reboot by itself and you should now have a jail broken iPhone with Cydia installed.
Step 17: Once booted into the device, launch Cydia, then go to Manage > Sources > Edit > Add, and type in the following: http://repo666.ultrasn0w.com and touch ‘Add Source’
Step 18: Cydia will now automatically update your sources by following a series of automated steps. After this is completed, search for ultrasn0w 1.2.1 in Cydia and install this app. This app will automatically unlock your iPhone so that you can use it with any carrier.
Step 19: Finally, restart your device and you should have a fully unlocked iPhone 4 running iOS 4.3.1.