Well, the Linux based Maemo OS I had in 2005 0r 2006 on my Nokia 770 was already promising, although the hardware was quite slow and limited, but it was an open system one would have root access to out of the box. Then it evolved into Meego, which was even better and was then employed by the Nokia N9. Nokia already had the OS to transition to from the old Symbian, but after the Microsoft deal, they scrapped it to adopt Windows Mobile, and the rest is history.
Maemo and MeeGo and other Nokia OSs were more coherent than Microsoft's phone OSs at the time, and Symbian would have had a long life on cheap devices. Smartphones were expensive back then.
https://en.wikipedia.org/wiki/Nokia_770_Internet_Tablet
https://en.wikipedia.org/wiki/Maemo
https://en.wikipedia.org/wiki/MeeGo
https://en.wikipedia.org/wiki/Nokia_N9