How to enable on screen virtual home, back, menu buttons on your android phone

If you have an android phone with phisical home, back, menu buttons and want to enable on screen buttons try this steps. Requires your device to be rooted and running Android 4.0 Ice Cream Sandwich or above. DO THIS AT YOUR OWN RISK!

• Using any file manager that has root access, go to System directory.
• Edit build.prop file in a Text Editor.
• Scroll to the end and on a new line input:

qemu.hw.mainkeys=0

• Save and Exit. Then Reboot.

If you want to Disable On-Screen Navigation Button, follow the steps above, but delete the previous line or input this line instead:

qemu.hw.mainkeys=1

I have tried on my Xperia arc S and worked well but buttons hide the bottom of main screen icons.
There is another way to use onscreen buttons. I found a really great application on google play. Overlay launcher starts a small line-button on bottom screen. You can define one touch to go back, two touch to go home and stay touch if you want to get menu.