Now that the iPhone's operating system supports 3D, I was wondering when the first CAD applications would appear. Today Halabe & Han tells me about NaviCAD for searching and viewing the Google 3D Warehouse on the iPhone. Warehouse models are created with SketchUp.
You control the view of the loaded model by moving the iPhone. Tipping the phone down rotates the model so that you see its top, for instance. More details here.
Purchase from the Apple Store, which requires iTunes installed on your computer. (I don't.)