Sn0wbreeze 1.7 for iOS 4.0 has been released. This jailbreak supports following iDevices
1. iPhone 3GS (Old bootrom)
2. iPhone 3GS (New bootrom having SHSH stored on cydia for 3.1.2 or running jailbroken 3.1.2)
3. iPod touch 2G (non-MC models)
4. iPod Touch 2G (MC models having SHSH stored on cydia for 3.1.2 or running jailbroken 3.1.2)
5. iPod Tocuh 3G (having SHSH stored on cydia for 3.1.2 or running jailbroken 3.1.2)

2nd, 4th and 5th will be tethered jailbreak, means you need to re-connect to computer whenever you reboot iDevice.

I have jailbroken iPhone 3GS(New bootroom having jailbroken 3.1.2, SHSH not saved for 3.1.2) by following these instructions.
Step 1. Download following software

1. iTunes 9.2
2. Payload Pwner-r3 for the 3GS
3. iBooty V1.3
4. LibUSB Installer (Step 4)
5. iPhone 3.1.2 and iOS 4 for iPhone 3GS
6. Download 7-Zip or another un-archiver

Step 2. Install iTunes 9.2

Step 3. Connect iPhone to PC and take backup of iPhone using iTunes. You can remove iPhone after backup is over.

Step 4. (Installing LibUSB)
Windows XP Users download this installer — LibUSB Installer. Install it as you install any other program.
Windows Vista & Windows 7 (32 Bit)
I am running Windows Vista 32 bit, I downloaded LibUSB from here. Right click on LibUSB installer(libusb-win32-filter-bin-0.1.12.1.exe), Go to compatibility tab and check “Run this program in compatibility mode for Windows XP (Service Pack 2) “. Press ok. Again right click on LibUSB installer (libusb-win32-filter-bin-0.1.12.1.exe). Click on run as Administrator option and install it. Windows 7 (32 Bit) can follow above instructions.
Windows Vista & Windows 7 (64 Bit)
If you are on Windows Vista (64 bit) or Windows 7 (64 bit), read instructions carefully.

Step 5. Extract iBooty-V1.3, Extracted folder will contain following files

1. iBooty.exe
2. irecovery.exe
3. readline5.dll
4. sn0w.img
5. wait.img

Step 6. Click on Payload Pwner-r3. It will ask for 3G[S] 3.1.2.ispw. Locate "iPhone2,1_3.1.2_7D11_Restore.ispw" file on the disk (Downloaded earlier). This will create a payload + iBEC. Save them in a location where you saved all above download and give folder a name say “payload”.
This folder will contain two files ibec.40 and iboot.payload, move them to the folder where you extracted iBooty-V1.3 (Previous step).

Step 7. Click on sn0wbreeze-V1.7 to create a custom firmware

1. Connect iPhone to your PC
2. Select Expert Mode and click on Blue Arrow at right bottom, Installer will now ask for OS 4.ispw, after verifying ispw, it may show a waring in case if you are on jailbroken 3.1.2 and don’t have SHSH for 3.1.2. Ignore this warning
3. Select general option and click on Next. This will show you an option window and first option “Activate The iPhone” selected. Check “Disable NOR Flash” (This is must for new bootrom)
4. If you are jailbreaking iPhone 3GS then all other options are implicitly checked (UI doesn’t show checked)
5. Click next and again next and then select Cydia(need for carrier unlock) and Rock(If you need it)
6. Select any custom app if you want them part of custom firmware and move to next step
7. Uncheck Boot logo and Recovery Logo and click on next(Blue) button.
8. You’ll get the same screen as on 3rd step. Select “Build ISPW” option now and click Next button.
9. This will create a sn0wbreeze_iPhone 3GS-4.0.ispw file on your desktop.

Step 8. Extract sn0wbreeze_iPhone 3GS-4.0.ispw created by sn0wbreeze with 7-Zip or another un-archiver.

Step 9. Grab

1. kernelcache.release (In root directory where you extracted )
2. DeviceTree.n88ap (\Firmware\all_flash\all_flash.n88ap.production\)

move these files to the folder where you extracted iBooty-V1.3 (Step 5) and rename kernelcache.release to kernal.40 and DeviceTree.n88ap to devtree.40.

Step 10. iBooty-V1.3 extracted folder will contain following files

1. irecovery.exe <-- Comes with iBooty.
2. readline5.dll <-- Comes with iBooty.
3. iBooty.exe <-- Comes with iBooty.
4. sn0w.img3 <-- Comes with iBooty.
5. wait.img3 <-- Comes with iBooty.
6. iboot.payload <-- Created with Payload Pwner.
7. ibec.40 <-- Created with Payload Pwner.
8. devtree.40 <-- Grabbed from Custom IPSW made by sn0wbreeze.
9. kernel.40 <-- Grab from Custom IPSW made by sn0wbreeze.

Step 11. Connect iPhone if you disconnected and run iBooty.exe and Select “Prepare Device for Custom Firmware”. Run the Process and if you see the image, you can proceed!

Step 12. Now open iTunes 9.2 and restore to the sn0wbreeze_iPhone 3GS-4.0.ispw by using Shift + Restore option.

Step 13. Wait for iTunes to complete restore process. After the process is finished, your device WILL NOT BOOT. Close iTunes and check your process list if iTuneHelper.exe is running then kill this process too. Now re-run iBooty.exe (tethered) and now select on “Boot It”.

Step 14. If all goes well it will boot!

To unlock iOS 4, follow step by step guide posted here

Some more tips if you are stuck in show boot image logo

1. Close itunes and Kill iTunesHelper from task list.
2. hold Home + Power button until screen flashing and automatic go into recovery mode
3. Again close iTunes detect recovery mode.
4. Run ibooty wait until everything is done.
5. Stuck on logo snow now. Now run iTunes then finally you got log screen

As discussed in previous post, a guide for jailbreaking iOS 4 on iPhone 3GS having 3.1.2 SHSH saved, is posted by iH8Sn0w. Jailbreak is not straight forward. You need to know iPhone 3GS completely. If you don’t know scripting then stay away from this jailbreak. Wait for some more time, there will an easy tool for all.
Follow the link to read about jailbreak.

Good news for those who have bought iPhone 3GS recently, No jailbreak available for such iPhone 3GS having new bootrom till now.
iH8Sn0w has developed a tool to jailbreak iPhone 3GS having new bootrom. Unfortunately jailbreak requires that you have your iPhone 3.1.2 SHSH blobs saved on cydia server. it is a tethered jailbreak so whenever you turn off your phone, you will need to re-connect it to a computer to be able to turn it back on. Originally this was not planned for release; however, iH8Sn0w has agreed to make it public.

Alright... If anyone has their 3.1.2 SHSH blobs, NOT 3.1.3. Then I'll see if I can produce a tool that will do this job... - iH8Sn0w

It may be possible that you are on 3.1.2 but your SHSHs are saved for 3.1.3. If this is the case then you are out of luck for now. I don’t know if anyone is working on that scenario.
A video posted by iH8Sn0w showing iOS 4 running on iPhone 3GS having new bootrom.

Sn0wbreeze 1.6 is almost ready for windows users. iH8sn0w will release it in 2-3 days. Sn0wbreeze supports:

• iPhone 3G/3GS (old bootrom/already jailbroken–NOT INCLUDING Spirit)
• iPod Touch 2G

Have a look on the video posted by iH8sn0w

Dev team has released PwnageTool 4.0 for iPhone 3GS on Mac. You must know few points before you start upgrading your iPhone 3GS

• You must own a mac
• Not have jailbroken previously with Spirit
• Have a hacktivated iPhone running iPhone OS 3.
• You have not upgraded to iOS 4

If you are running jailbroken iPhone OS 3.0, 3.1.1 or 3.1.2. You can upgrade to iOS 4 by following the instructions given here .
After you upgrade, let us know your iOS 4 experience.

With the launch of iPhone OS 4, your iPhone (3G, 3GS, 2nd and 3rd generation iPod) will become more power full than ever. Here are keynotes of the presentation

Most talked new features:
1. Multitasking : You can run more than an application simultaneously. So now you’ll be able to make a Voice over IP call while playing a game or checking email, while preserving battery performance.
2. Folder : Organize application icon into folders with simple drag-and-drop. Get faster access to your favorites and manage up to 2160 apps at once, many more than the current limit of 180 apps.
3. Better email: A unified inbox for all your email accounts. No need to switch from a account to another.
4. iBook: Buy books online, easy flip of pages.
5. SSL VPN Support: SSL VPN support in iPhone OS 4 gives users another way to securely access enterprise resources. These new protocols can even be leveraged to connect seamlessly to a corporate network via VPN on Demand. Forthcoming apps from Juniper and Cisco will support SSL VPN on iPhone.
6. Wireless App Distribution: iPhone OS 4 enables enterprises to securely host and wirelessly distribute in-house apps to employees over Wi-Fi and 3G. Apps can be updated without requiring users to connect to their computers.
7. iAd : Developer can make revenue through using iAd nicely integrated with Application.

Other features

• Game center
• Tap to focus video
• Larger fonts for e-mail, texts, and alerts
• 5x digital zoom in camera
• Bluetooth keyboards
• Spell check
• Persistent Wi-Fi
• iPod out
• Customizable wallpapers for the home screen
• Search text messages
• Choose image size in mail messages
• Recent Web searches
• Create playlists
• Gifting of apps
• Birthday calendar
• Wake on wireless
• File and delete mail search results
• Web search suggestions
• Rotate photos

In this tutorial you’ll jailbreak/unlock firmware 3.1.2 for iPhone 3GS using BlackRa1n. Before continuing, please make sure that you are on 3.1.2 firmware and 05.11.07 baseband. Go to setting => General => About

If you are running some older firmware then upgrade to firmware 3.1.2.

Step 1. Go to http://www.blackra1n.com/ url, download BlackRa1n depending upon your computer (PC or Mac). If you are downloading using safari then your download will be in zip format. Unzip it.

Step 2. Connect iPhone to the computer and make sure that iPhone is turned on.

Step 3. Double click on blackra1n icon that you downloaded in step 1.

Note: you may get warning depending upon your operating system after double clicking on blackra1n icon. Click on Run.

Step 3. You will see a large button (make it ra1n) on a window. Click this button.

Step 4. Your work is done now. Geohot will do the rest. iPhone will enter in recovery mode.

Step 5. Wait for 5 mins. You’ll see jailbreak done screen. Your iPhone will reboot now.

Step 6. Unlock iPhone and check your screen. Your iPhone is jailbroken. You’ll see blackra1n icon in your iPhone’s window. Tap on the icon.

Step 7. [Optional] Go to Setting => General => Auto-Lock and make this value Never.

Step 8. Choose installer you like most and choose snow if you would like to unlock your iPhone for all the carriers.

Note: You will need internet connection on your iPhone to perform step 8.

Step 9. Wait for some time. You will see a log window after all the installations are finished.

Step 10. If you want to remove blackra1n icon form iPhone then tap on uninstall blackra1n. You’ll see delete button. Tap on this button.

Step 11. [Optional] If you have changed Auto-Lock time in step 7, then reset this value to the value you like.