The old Symbian* smartphones.
Just a detail, I know, but as far as I remember, I changed few Symbian devices before the iPhone came out and I hopped over Android soon after.
I can't really recall there being any Windows phones back then. This is just how popular Symbian was in that period of time. If there were any Windows devices (forgive my ignorance), they were definitely not nearly as popular to make a mention of iPhone killing them instead of e.g Symbian ones.
Just my 2¢, but the crux of your argument doesn't change, so you got a +1 from me for it. :)
On the other hand if you are in the business of selling embedded development education to newbies, then you need to realize that Arduino is outcompeting you - like iPhone destroyed the old Windows smartphones.