Miniaturized Human 3D Motion Input

Imagine that you are sitting on a train, standing in a queue or walking down the street. You are, like a majority of people in the world, carrying one or more mobile computing devices. It could be a mobile telephone, a portable media player, a personal digital assistant (PDA) or a portable gaming console (e.g. Nintendo DS, Sony Playstation Portable). Your particular device has 3D graphics capabilities, and you have some application – perhaps a game, a navigation tool or a computer-aided design (CAD) model – that needs 3D input. How do you provide 3D input to your device as intuitively and quickly as possible, preferably using only one hand? And how can you provide the input while standing and without needing to use a stable surface such as a table or wall?