For presentation purposes, I need to visualize a process that involves rotating the smartphone in 3D-space. Hence, I am looking for a drawing tool (or a way), which has smartphone graphics (preferably generic) that can be individually rotated around all 3 axis.
Have you thought about SketchUp? I have found it easy to learn and use, and it is backed by a pretty big 3D model repository. You can export 2D graphics from it too.
Sketchup: http://www.sketchup.com/ (you can download the free Sketchup Make and try it out)
Sketchup repository: https://3dwarehouse.sketchup.com/index.html