These instructions were found here: "http://p900themes.altervista.org/tutorial.htm"
"Going to control panel - > display - > power tab, you can set power save function for visualizing on the black screen, after a lap of time that your phone remains inactive to flip closed, a digital clock. It's possible to personalize the clock replacing the font whom it uses by default, with two mbm files to add in C:/system/data. These two files are SCREENBLANKERNUMSLARGE.MBM and SCREENBLANKERAMPMLARGE.MBM. The first one composed by 10 images bmp 24x47 pixel, 24 bit, 96dpi, on black background and with the numbers from 0 to 1 with the new font chosen white colored. The second one instead composed from 3 images bmp 14 x 47 pixel, 24 bit, 96dpi, on black background respective with acronyms "AM", "PM"and ":" using the same font as told before. Once you've got aech single bmp file,
you must compress them in the two aforesaid files in mbm format with the application mbmconv.exe and transfer them in C:/system/data on our phone...that's all!!!"
I have not tried this and take no responsability for any problems.
Sitting still, doing nothing, spring comes and the grass grows.