Tech talk Digest

Blacksn0w RC2 has just Released for iOS 4, this release is based on the original unlock tool from geohot, and the binaries which were released from couple days by MSFT GUY for 05.11.07 baseband on iPhone 3GS, running iOS 4.0 GM. Follow the step by step guide After the jump..

Here's the description mention in the site:

Use on Modem Firmware 05.11.07 ONLY!
V1.2: Support for 4.0 GM. Backwards compatible to 3.1.2/3 as well. V1.1: MyWi tethering fix
Geohot’s unlock for 3.1.2/3.1.3/4.0GM on the iPhone 3GS (and probably 3G). Please donate at http://blackra1n.com/ if you enjoy.
With 3.1.3 & 4.0 GM patch (when needed) by msft.guy. Packaged by Pushfix.info
This is an unofficial release but Geohot HAS given me permission to redistribute blacksn0w. All known issues with WiFi loss and boot loops seem to be fixed.  If it doesn’t work for some reason, you should still get the SpringBoard. This allows you to uninstall if necessary. It is a little slower to boot because of the increased safety of the release. A 3GS boots to cell connection established in about 90 seconds in iOS 4 now (50% slower than 3.1.X).
Improvements may be made in the future.

Note: This guide is used to unlock your iPhone 3GS on iOS 4, 05.11.07 baseband using blacksn0w RC2. Also Blacksn0w binaries are a little buggy, and this will result in your phone taking at least 90 seconds on every reboot to catch carrier signals.

Step 1: First, You will have to Jailbreak your iPhone using PwangeTool, Step-by-Step guide from Here.
Step 2: Now you can get Blacksn0w RC2 from Cydia,To do this Start "Cydia" on your iPhone then Go to "Manage" tab at the bottom, Now click on "Sources" as shown in the screenshot below:

Step 3: Click on "Edit" then on "Add", Then you will be promoted to enter a url source type "http://cydia.pushfix.info" then click on "Add Source"
Step 4: Now Cydia will start Installing your new source, just let it happen!
Step 5: Now, in Cydia search for "blacksn0w RC2 for iOS 4" and install this App. This App will automatically unlock your Device.
 Step 6: Simply. Restart your Device, and wait at least 90 seconds for your iPhone to get the signal of your carrier.