Hi Mang mel.
The process described in the opening post of this thread covers the Z500 model, I believe. It seems to be bona-fide; I downloaded the software and it appeared to run ok, but unfortunately for me the Z400 wasn't supported.
If the Z500 is anything like the Z400, then it CANNOT be unlocked with a simple typing in of a code - believe me I've tried, and only succeeded in freezing my SIM card along with everything else! A more complex process is required, involving software and connecting your phone to a computer. If you don't think you are up to doing this, then take your phone to a professional!
Which is what I ended up doing!!!
So, I can thoroughly recommend ' unlock-my-phone ' who sells on Ebay. They also have a proper website, tho' I forget what it is - it could be similar. I can check if anyone is interested, as it's on a contact email somewhere!
I needed everything doing to my phone after I'd finished with it (!): unlocking, unfreezing the SIM, and debranding. I was quoted