Usually you need to find a site like Polish SimLock24.pl - which provides paid unlock codes.

There is a brute-force method to be done at home with good PC (requires good graphics card). It's well described here:

http://nokiahacking.pl/simlock-jest-...15.htm#p581609

I can confirm that such sites on what you pay work - I unlocked my Samsung Omnia HD running Symbian S60v5 locked to Orange via SimLock24.pl. After flashing a not-Orange-branded firmware, it turned into a general Polish Omnia HD, without any Orange traces