Not sure about Orange's customisation, with Vodafone there was 1 flash theme (Orbit) - basically the menu's are customisable with flash - e.g. the main menu icons can be changed: in orbit a little ball of light spins around the icon you have selected, and the phone vibrates a little as you select things and move around: see here for some screenshots (
http://www.expansys.com/ft.aspx?i=136914&thread=96)...
They look pretty fun and I'm sure there's loads you could do, maybe I will have to teach myself flash