proper way to JB 3GS (old boot) on 3.1.2 to 4.2.1, and keep unlock?

[Madman604x]

so im kind of confused right now as to how to update to 4.2.1 on my old boot rom 3GS, which is at 3.1.2.

do i use redsn0w to update to a tethered JB while keeping my old BB, then greenpois0n to untether? then ultrasnow to unlock?

advice?

[Simon]

To preserve your baseband you will need a custom 4.2.1 made with pwnage tool.

[Madman604x]

i don't have a mac.

[Simon]

Then you will need to google for a custom firmware. That is the only way to preserve baseband on a 3GS.

[Madman604x]

ok. how about if i just use the official 4.2.1

is do i just use GP then ultrasnow?

or is it crucial to keep my old BB?

[Simon]

You wont be able to unlock if you update to a regular 4.2.1 firmware. At least not without updating to the iPad baseband which you dont want to have to do.

[Madman604x]

so it looks like a custom FW is my only choice to avoid using the iPad BB, which is irreversable.

Thanks x98car

[Simon]

no prob