There isn’t any working tool to unlock iPhone OS 3.1.3 with baseband 05.11.12 only those who have upgraded using PwnageTool  3.1.5 or Redsn0w 0.9.4 can use ultrasn0w 0.92 to unlock iPhone 3G & 3GS with 3.1.3 firmware. We had also reported about a new exploit found by sheriff on which iPhone dev team are already working, it may take some time to work out into successful unlock tool for 3.1.3 baseband 05.15.12.

Geohot fans might be missing Blacksn0w as it doesn’t work with iPhone 3.1.3 also Geohot has no plans to update tool to make it compatible with iPhone OS 3.1.3 baseband 05.11.07. Well do not worry a guy named msft.guy has found fix for blacksn0w to unlock iPhone 3.1.3 Baseband 05.11.07.

He has also posted reason why blacksn0w is failing to unlock iPhone 3.1.3 since it searches for function to patch by searching the binary for a reference to string “SIM is not supported”. In iPhone OS 3.1.3, Apple has replaced the same function in a way that it now uses the string “Verified”.

Since the location to patch is determined by instruction search&replace, the said patch still works in iPhone 3.1.3 after changing the string and its length in Blacksn0w binary.