I'll do the upgrade from ios 4.1 jailbreaked (on an iphone 3g with a foreign locked sim) without updating the baseband. My baseband is 05.14.02 (bootloader 5.9). So I should to obtain an iphone 3g ios 4.2.1 jailbreaked with the 05.14.02 baseband (I'm not interested to use it for phone calls).
I would to know what I have to save before the upgrade to revert to the original state (ios 4.1 jailbreaked) in case of failure.