Redsn0w is a popular jailbreaking and unlocking alternative to blackra1n for both Windows and Mac. It can jailbreak and unlock iPhone OS 3.1.2 and 3.0
All iPhones and iPod touch are supported except the iPod touch 3G. For the latest iPhone 3GS models and iPod Touch MC models, the process is still tethered. Redsn0w 0.9 is still in beta and is available in both Windows and Mac versions.
Redsn0w also enables users to personalize iPhone firmware’s with customized boot and recovery logos without having to use iTunes as there are no custom IPSW files involved. If other jailbreaking tools such as blackra1n, PwnageTool and sn0wbreeze didn’t work for you, you can always give redsn0w a try to see if it solves all your problems.
Download Redsn0w 0.9 beta 3 for Windows and Mac
Download Redsn0w for Windows
Download Redsn0w for Mac
The process to jailbreak remains same. Open up iTunes. Press Shift and click restore. Browse for the ipsw file you have on your PC. iTunes will restore the iPhone to 3.1.2. Once the restoring is complete, open redsnow and browse for the ipsw file. Choose ‘Install Cydia’ and ‘Unlock’ options. In case you don’t have the bootloaders, download them here and specify their locations in the wizard. Switch off your iPhone and click next. Follow the instructions to enter the DFU mode.
It will now start the jailbreaking process. Do not interrupt the process and wait for it to complete. Once it completes, you would be having a jailbroken and unlocked iPhone 3.1.2 with you!