RiM basically killed off a big chunk of the Nokia market, as it did for Windows CE as well.
By the time the original iPhone came out, Nokia hadn’t really put out anything to capture the mindshare in a while. They were severely hampered by the split of their Symbian lineup (S30,40,60,90) and unable to adapt to the newest iteration of smartphones.
They’d never have been able to adapt to compete without throwing out Symbian, which they held on to and tried to reinvent. Then there was the failure of MeeGo.
Nokia would have been in the same spot they’re in today regardless of Microsoft. They’d be just another (sadly) washed up Android phone brand. Just like their biggest competitors at the time: Sony Ericsson and Motorola.
But at least we got a lot of Qt development out of it.