I unlocked my Z300 (net lock) yesterday, within a few minutes! I found the solution here and I'm so happy I can use any sim card with my Z300. The only thing you need is a small piece of software and USB cable (supplied with the phone). It will read this code which you will use to unlock your Z300.
Download this file, unrar, read "manual" and after you obtain the MCK code, on you phone still without sim enter #7465625*638*MCK Code# = Disables Network Lock
Works great!
Does anyone know how to upload java apps to Z300?