You have to be on firmware 3.55 or lower if not, you'll need a Progskeet or E3 Flasher, if it's a slim you can use the E3 Flasher that requires no soldering but the newest slims can't be jailbroken at the moment. So if you buy it brand new, chances are, you aren't going to be able to jailbreak for quite some time, if they figure out how to run older firmware on them.