I think they're embedded in the firmware.
If you want to prevent users changing them you could set '
Oh yes you are right. Initially i thought that will work but it did not turn out to be true. Somehow, user still able to change the background setting. Did you tried that before?
I've tried it on older phones (e.g. 79xx) but it didn't work. I figured it must be firmware dependant, and if it worked on any you would imagine it would work on the new models.
I guess not :-)