Hello! I bought one of these a few weeks back so I`m hoping that it came with the same player as mine - a GDVD135. If this is the case, then I have found the hack!
Turn on the player and eject the disc tray.
On the remote, type 2812, followed by enter.
This gets you to the engineers menu.
Press down until you reach COUNTRY CODE and press enter.
The current region code will change to four dashes (----)
Input one number (0=Region Free, 1=USA 2=Europe, etc) and press enter again.
The new region code will now be displayed.
You can exit by just pressing the eject button once more.