unlock method help!

[chenzero]

Hello,
a Nokia 6020b mobile is restricted and I had tried some code
but they donot work.

I heard that 6020b can be unlocked by cable solution,
could anyone give some details on howto?

and, I also interested on how the carrier
locks the mobile? the encryption method is specific to each vendor or
standard?
Thanks for your help!
chz.