If i upgrade to 4.2.1 then in dat case can i still get my phone unlocked and jail broken.....???????????????

I somehow resetted the settings ( plz dont ask me why ) now tring to download firmware ipsw version 4.0.2 on iphone but cannot. After itunes tries to extract the software it gives a msg saying the iphone " iphone " could not be restored. This device isnt eligable for the requested build; Now...