A recent article in Machine Design magazine discusses Autodesk's beta app for downloading interactive, 3D models to the iPhone.
SolidWorks also has its version. At SolidWorks World 2010, a 3DVIA application engineer used my 3G S iPhone to take my picture, installed 3DVIA Mobile on the phone, and then used the app to download a 3D model of the "Ghostsniper Hot Rod Truck." He sized the model and placed it in my hand. Click on image to see an enlarged view....