I am trying to JB a 3GS I just bought from the store. I googled and am planning to use Sn0wbreeze but it says " One thing which is to be noted here is that it will work with iPhone 3GS only if it has the older bootrom (non-MC model). iPhone 3GS users who have upgraded to the stock 3.1.3 are still out of luck" What are they referring to as the old bootrom? The one I have is factory so 05.12.01. Can I just to a straight JB?