tried this a while ago.
-display won't work (works after i put in the K800i display driver)
-joystick only works for left and right
-camera works but after taking a pic it's not stored in the file manager
-flash theme's/wallpaper work
-M2 and mediaplayer work too
-flashing to a K770 has similar problems
-flashing to w850/W880 is even worse, no m2 support and malfunctioning keys
you can only flash it to a K810 if you want a perfectly working phone, so please don't tell lies here. tell it as it is. other users may want to try this only to find out that the phone will be buggy
it would be perfect if SE would make a K800I like walkman phone. seriously K800i is a beautiful phone. imaging how a walkman version would look like :)