Guys, this is some trick you can do with your friend's 5800.

Take a screensnap of the homescreen, and then open the screensnap file. The opened file will look exactly like the homescreen. Then give back the phone without closing the image file.

Actually, this morning I accidentally snap the homescreen with "Use screen keyguard  switch..." message. Then during lunch, I open the Gallery to watch some vid clip and accidentally opened the snapped images (both vid clip and image have black thumbnails). Because video usually take a while to open, after I open the file, I just turn away to do other thing.
When I look back I saw the screensnap image (I don't reliaze it a screensnap). So, I slide the keyguard to unlock key (I thought screen is unlock) but the screen turn off. When I slide again, I saw the images again (still not realize). After I click the screen, then I realize the zoom slide and back button. If not, I will keep slide the keyguard.