http://ubuntuforums.org/showthread.php?t=2072040

Re: VNC on xubuntu 12.04

    so after installing x11vnc I ran the following,
    sudo x11vnc -storepasswd yourpasswordhere /etc/x11vnc.pass
    sudo chmod 744 /etc/x11vnc.pass

    then I added the following to /etc/lightdm/lightdm.conf
    greeter-setup-script=/usr/bin/x11vnc -auth /var/run/lightdm/root/:0 -noxrecord -noxfixes -noxdamage -rfbauth /etc/x11vnc.pass -forever -bg -rfbport 5900 -o /tmp/x11vnc.log

    I’ve tested it with logouts and reboots and it works fine with one minor flaw of disconnecting the active connection when you log out and having to reconnect once its at the login screen

Start it with: x11vnc -display :0
or x11vnc -display :0 -rfbauth .vnc/passwd

Afterwards I can connect with phone through RealVNC connecting to port 5900 (machine.IP:5900)