I might be wrong. But I do not see any way to tell the email client in the Email Opens,,
With following, we can tell if the click-thrus are from a device or not....
If the email recepient clicks on the 'view as a web page' or any other link in the email, that information is captured. But it is captured in the visited webpage 'Activity log' for that lead.
This value is available as a constraint named 'Browser' to create smart list such as Visited web page 'Any link in that email'
Thus you can write a smart list / or a report with filter 'visited webpage', select that web page and Browser contraint contains 'iPhone' or any of the values such as
iphone|ipad|ipod|android|blackberry|mini|windows\sce|palm
The User Agent / Browser contains
User Agent:
Mozilla/5.0 (Linux; U; Android 2.3.5; en-us; SAMSUNG-SGH-I897 Build/GINGERBREAD) AppleWebKit/533.1 (KHTML, like Gecko) Version/4.0 Mobile Safari/533.1
for my cellphone.
Hope this helps
Rajesh