Can you unlocked iphone 3gs on 4.2.1?

[kris2pe]

I know you can now Jailbreak on 4.2.1 using Greenp0ison.
But can you unlocked it safely?
Thank u!

[iYeow]

if you restored to stock 4.2.1, then u have a non unlockable bb, to unlock , u must update to iPad bb. if you currently do not have bb of 05.14 or 05.15 , then to be able to unlock, you must restore to custom fw to preserve your current unlockabke bb at 4.2.1.
note: old bootroom 3GS cannot be jailbroken by greenpoison,
use redsnow to jailbreak after restoring to custom fw of 4.2.1 if you want to preserve your bb
new bootrom, u can restore to custom fw and jailbreak with GP to get untethered jailbreak

hopefully this is not too complicated to understand

[kris2pe]

I'm still 4.01. And yeah that was complicated explanation.
and I am planning on upgrading on the latest version what should I do?
How can I tell if I have the old or the new bootrom?