The good thing about AMOLED screens is that when a pixels display a true black color (#000000) it's actually completely turned off that pixel, in fact displaying true 480x800 black image on the SGS screen resemble turning the screen off. so i was thinking what if the screen was completely black except for few pixels in the coroner that are green to indicate miss calls, the screen will only consume power to keep these few pixels on, the rest of pixels will not consume any power.
To demo this, i made this 480x800 image with all pixels black except for 9 green pixels on the top left corner, you can save it and try it in your SGS full screen, as for the power consumption, the screen have a total of 480x800=384000 pixels, of which only 9 is on, so 9/384000=0.002% of the screen power only consumed to keep these 9 pixels on.