THNX for the clarification bro. cheersthis fix is for people who followed the recommendations of the dev team and stayed on the pwnagetrain (but bought their phone on 3.1.2 or 3.1) or those who used blackra1n to jailbreak then upgraded safely to 3.1.3 via either PwnageTool or sn0wbreeze (unsupported unofficial windows clone of pwnagetool)
these iPhone owners (3G and oldbootrom 3GS) have ended up with 3.1.3 via custom ipsw and baseband 05.11.07. Now they can use blacksn0w unlock.
There is not a direct jailbreak for 3GS accidentally upgraded to 3.1.3. Unlock for 05.12.01 will also likely never exist.