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It's so sad that the Iphone OS 3.1 couldn't crack bay jailbreak. I've done by myself on the Iphone OS 3.0.
This artical maybe helpful for you. Have fun and good luck.
The iPhone 3.0.1 update was recently released. If you want to jailbreak any iPhone running on  iPhone OS 3.0.1, you must use redsn0w 0.8. This post will show a step-by-step tutorial on how to jailbreak iPhone 3.0.1 with redsn0w.
Note:

1. redsn0w only recognizes iPhone 3.0 firmware (not 3.0.1 yet!), although you are running firmware 3.0.1 you must still download iPhone OS 3.0 firmware for your device.
2. The recent iPhone 3.0.1 update does not fix the iPhone 3GS hole, so it’s safe for iPhone 3GS users to update. If you downloaded a purplera1nday file or your iBec or iBSS for iPhone 3GS you don’t need to redownload it because it’s identical in this update.

First you must download redsn0w for Windows, Mac, or Linux

Download redsn0w

You can download the current redsn0w software from any of the following links:

• redsn0w 0.8 Windows Download (Direct Download)

• redsn0w 0.8 Mac Download (Direct Download)

• redsn0w0.8  Linux Download (Direct Download)

redsn0w 0.8 works for Phone 3.0.1, iPhone 3G 3.0.1, iPhone 3GS 3.0.1, iPod Touch 3.0, and iPod Touch 2G 3.0.

1. Download the iPhone OS 3.0 IPSW file for your device and save it to your desktop. Here are the file names for each device, make sure you have the right one:

• iPhone 2G – filename: iPhone1,1_3.0_7A341_Restore.ipsw [download link]
• iPhone 3G – filename: iPhone1,2_3.0_7A341_Restore.ipsw [download link]
• iPhone 3GS – filename: iPhone2,1_3.0_7A341_Restore.ipsw [download link]

2. Open the redsn0w 0.8 application to jailbreak iPhone 3.0.1.
4. Locate your device’s IPSW file that you downloaded in step 1 and click Open.
5. The redsn0w window will have the “IPSW successfully identified” message. Click the Next button to continue.
6. redsn0w will ask you to “Please select which options you would like to have“. Make sure the Install Cydia box has a check mark and then click Next.
7. redsn0w will ask you to make sure your device is both OFF and PLUGGED IN to your computer. Make sure you plug in your device in to your computer and then turn it off. Click Next once you have done this.
8. redsn0w will now ask you to connect your device in DFU mode, you must do this properly to jailbreak iPhone 3.0.1.

1. Hold down the Power button for 3 seconds
2. Without releasing the Power button, also hold down the Home (bottom center button) for 10 seconds
3. Without releasing the Home button, release the Power button BUT KEEP holding the Home button for 30 seconds

• If you don’t do this properly you will get a DFU Mode Failed message and you’ll have to go back to step one.

9. Once your device has successfully entered DFU Mode, redsn0w will show the following message: “Please wait while your device is being jailbroken. Waiting for reboot.” Your device should reboot after this. If redsn0w is stuck on Waiting to Reboot, unplug your USB cable quickly and plug it back in. The jailbreaking process should continue after tha.
10. Once your device has rebooted redsn0w will start uploading the RAMDisk and kernel.
11. After everything has been successfully uploaded to your device, redsn0w will have; the “Done!” message. Your device will now reboot and you should see the Cydia app on your SpringBoard. Your iPhone is now jailbroken!

Now we use Cydia to install untras0w

Update: ultrasn0w has been released by DevTeam! ultrasn0w is an iPhone 3.0 software unlock for iPhone 3G users only.
Here is how to install ultrasn0w:

1. Jailbreak your iPhone 3G 3.0: use redsn0w

2. Go to Cydia and add  repo666.ultrasn0w.com to your sources

3. Reboot your iPhone 3G (T-mobile users should disable 3G before using ultrasn0w)

4. Enjoy your iPhone 3G unlock, thanks to the Dev-Team that worked hard on it!

With the new OS 3.0 update a lot of people are stuck without an unlock, and they’re waiting for the iPhone Dev Team to create one. On Friday the iPhone Dev Team plans to release ultrasn0w. Ultrasn0w is the name of the Dev Team’s new iPhone 3G unlock software and it’s 100% free just like all the other Dev Team tools are. ultrasn0w will allow you to unlock your iPhone 3G on the new iPhone OS 3.0 firmware. Of course to unlock your AT&T iPhone 3G and install ultrasn0w you will need to jailbreak your iPhone 3G. The jailbreak does not appear to be out right now but Dev Team is working hard to bring it out for us. Please have patience and let the Dev Team do their work! Don’t ask when it’ll be out. I’ll make a post with download links and information on QuickPwn.com homepage, forums, and also update twitter, YouTube, send e-mail notifications to those who subscribed.
Waiting for ultrasn0w? Here’s what we know about it so far.

• It’s safe to update to the current iPhone 3.0 baseband – ultrasn0w will work with it, but for future updates such as firmware 3.0.1 (or whichever # the next firmware is) you should hold off on updating and check here first to see if it’s safe to update. Apple may be able to make a baseband update that permanently locks your firmware just as they did with firmware 2.2.1 users.
• ultrasn0w will only work with iPhone 3G – iPhone 2G users can still unlock their iPhone using BootNeuter
• Just like yellowsn0w, ultrasn0w can be installed from Cydia (Repo URL has not been announced yet)

More information and a guide on how to unlock iPhone 3G with ultrasn0w will be posted once Dev Team has released ultrasn0w!