I purchased a used iPhone 3G that I want to use with my T-mobile plan. TinyUmbrella shows that the phone is currently running firmware 3.1.3, with baseband 0.5.12.01-6.4_MS32.
I think the tutorial at iClarified - iPhone - How to Jailbreak Your iPhone 3G on OS 3.1.2, 3.1.3 Using RedSn0w (Windows) will work for me, but I have a couple of questions. First, the firmware downloaded from the iClarified site is 3.1.2. Will this work running agains 3.1.3?
I found a version 3.1.3 ipsw at Greenpois0n.us. Assuming I can trust this site, would I be better off with that file? (I couldn't find a link to greenpois0n on these forums, and there is also a greenpois0n.com. Are either of these legit?)
I would also like to upgrade to firmware 4.2.1. I can't run pwnage, since I have no access to a Mac, and winpawn seems to be quite out of date. I downloaded the 4.2.1 ipsw from iClarified. If I use shift-restore from iTunes, can I load 4.2.1 or will that also update baseband? And is there any way to tell in advance what baseband that ipsw will load?
tl;dr: What is the best procedure to jailbreak and update this phone to 4.2.1 without updating baseband?