Blacksn0w! Procedure to Jailbreak/Unlock

blacksn0w is a free unlock for the latest iPhone 3G and 3GS
blackra1n is a super simple jailbreak used to install unlock
new visitors, go to blackra1n.com download and have fun

blackra1n RC3 is also live for both Windows and Mac!!! Clean firmware 3.1.2 and baseband 05.11.07 are recommended.

Updates:
Unlock!!!
Hacktivation
Keep legit activation if activated before running app
15 seconds faster, you'll feel it
Tiger + PPC support

Go to blackra1n.com to download
For support, blackra1n.support at gmail...but read this first

blacksn0w is also available on Cydia, add blackra1n.com as repo
requires firmware >= 3.1 and baseband 05.11.07

It appears some users are having wifi issues. Try a "Reset Network Settings". If someone can come up with a way to replicate wifi issues, I will investigate further as I have not yet seen these issues firsthand. Also, this just enables custom MobileConfig files. To fully enable tethering, go here on your iPhone and download a MobileConfig file for your carrier. Watch out for carrier fees for tethering.

Push and YouTube issues are caused by hacktivation. The dev team has a fix for YouTube which they are posting on Cydia shortly.

iClarified has made some nice tutorials:
Windows
Mac

From Geohot's Blog


Procedure here:

This entry needs translation. To help us and submit a translation please click here These are instructions on how to jailbreak and unlock your iPhone 3G and 3GS using BlackRa1n and BlackSn0w for Windows. These instructions will work with the latest 3.1.2 firmware, the 05.11.07 baseband, and iPhones which require hactivation. If you have already jailbroken following these instructions to unlock will be easier. For those with a new iPhone 3GS (updated Bootrom), BlackRa1n only supports a tethered jailbreak. This means that once jailbroken you should not let your battery die. If it does die you will need to reconnect it to the computer and use BlackRa1n to boot it. Before continuing make sure you are on the 05.11.07 baseband by following this tutorial. If you are not please update your firmware to 3.1.2 using iTunes before continuing. You can find the Mac version of this tutorial here. Ok lets begin... Watch the Video! For your convenience this tutorial is available in video format also. Click the Watch It button to view the tutorial! Step One Open your web browser of choice and navigate to http://www.blackra1n.com. Click the Windows logo at the bottom of the screen. Step Two When prompted save the download to your desktop Step Three Then double click the blackra1n executable file from the desktop to launch the program Step Four Make sure your iPhone or iPod is connected to the computer then click the large make it ra1n button Step Five You iPhone will now be placed in recovery mode. You will see a picture of GeoHot that replaces the regular recovery mode screen on your device. blackra1n will run and then your device will reboot. A popup message will appear informing you that BlackRa1n is free software and if you appreciate it you can donate to GeoHot at geohot@gmail.com. Step Six Once your device reboots it will be jailbroken and you will notice a blackra1n icon on the Springboard. Make sure you have an internet connection and press to launch the application. Choose the installer application of your choice then press to select sn0w if you would like to unlock your device. Press the Install button at the top right of the screen to begin. BlackRa1n will begin to download and install the package you selected. If you chose to unlock device using blacksn0w you will be presented with a Post Install log for sn0w. CommCenter will be restarted and there is no need to reboot. If your carrier doesn't support 3G then disable it. Press the Close button to continue. Step Seven Once complete BlackRa1n will respring your iPhone and you will find the installer package of your choice on the Springboard. Step Eight Once you have confirmed your installer package is working correctly you may use the Uninstall blackra1n button inside the BlackRa1n app to remove it from your springboard. ***THANKS: A big thanks to Geohot for making this jailbreak possible. Also thanks to those who contributed to making it a success. You can donate to Geohot using the button below. Please note these donations go to Geohot and not to iClarified.