I think it will depend more on the specific components that you build into your course. Again, Moodle allows linking to a Flash webpage, but this won't plan on iDevices. If you link to a PDF file, or PowerPoint file, and the smartphone doesn't support these programs, you are out of luck.
Having said this, all of the internals of Moodle should work quite well (I cannot say perfectly because I haven't tried everything myself) on many smartphones.
The key is to experiment on your own, and then listen to your users about what they find is and is not working.