Finally got around to trying this, and enjoyed it!
I definitely love that you use the numpad layout for controls, but I think it could be done a bit smoother - it is a bit confusing that the "continue" button in the customer dialog is the same as the "up" button in movement mode. I think an easy way to fix this would be to scrap the movement mode and instead dedicate two buttons to moving through modes (like 4/6). Then in each view 7/9 could be left/right so that flipping through the index, selecting an ice cream, selecting extras and selecting a price used the same two buttons everywhere, and 5 always meant confirm selection.
I enjoyed your graphics and sound, and applaud that you chose a font that was actually readable!