John,
I think you will be fine on any device with real web browsing capabilities. The Blackberry unfortunately, except for maybe the newer Bold model that runs on 3G in the States (not sure what networks it utilizes in Europe) are probably going to be problematic. But, if you make sure your parent item opens a page that then contains links to all of the would be dropdown items, I would say that you have provided the same functionality and hope your client would see it that way too. I really think that is the only happy medium in this case.
Good luck,
Brian