iPhone users who have upgraded their phones to latest iPhone firmware 3.1.3 are now facing problems with jailbreaking as well as unlocking. iPhone hackers are waiting for Apple to release iPhone 3.2 upgrade, and not releasing their tools for 3.1.3 firmware.
This is really frustrating for end users, but there is no need to worry. MSFT Guy has resolved the issues in Blacksn0w. He has released a patched version of this tool which only works with iPhone OS 3.1.3 Baseband 05.11.07.
Download Blacksn0w for iPhone 3.1.3 Baseband 05.11.07
You can add this repo – http://cydia.pushfix.info/ and install the Blacksn0w RC2 package. Also, read the important instructions given for Blacksn0w – Link
Please note that this tool is still available in RC version and its final version is yet to be released. So, use it at your own risk!
If you have updated to Baseband 5.12.01, you will have to wait for some more time.
Read: How to unlock iPhone 3.1.3 Firmware?