With so many jailbreak options and after trying greenpoison with no success,which jailbreak is the best for my iPhone 3G on 4.2.1(8c148)with firmware 05.15.04 thanks for any help.
Strangely, I did this exact jailbreak on my girlfriends phone yesterday (3G on 4.2.1), I used Redsn0w. The only thing to remember if you're on Windows 7 or Vista is to run as administrator and in XP compatability mode.