From the bottom of the summary here: http://en.wikipedia.org/wiki/Symbian#integrated_Symbian_plat...
We get: http://www.appleinsider.com/articles/09/08/21/canalys_iphone...
Symbian OS had 50% of the smartphone market as of August 2009. And 50% of the market in that dataset is a majority - probably a good enough a citation for "C++ was the mobile world" when you consider what that would have looked like before the iPhone.
For some reason, people here seem to think that iPhones and other fancy devices are all there is out there.
I originally wrote Hecl to run on a Nokia 3100, which came out something like 5+ years ago, and was certainly not top of the line then (it was about 100 euros, IIRC).