The last Nokia N-Series phone that will be using the Symbian Operating System is Nokia N8. All new and upcoming Nokia N-series phones will be using MeeGo instead. MeeGo is an open source mobile operating system that is based on Linux. MeeGo is the result of the joint efforts of Nokia (Maemo) and Intel (Moblin).
Of course, Symbian will still be made available for the budget phones of Nokia.
The decision to drop Symbian on Nokia N-Series devices is because they’re behind in the smartphone market.
As of the moment, MeeGo has developer images available for ARM-based Nokia N900 and for Intel Atom-based handsets. Aside from handheld devices, MeeGo also supports other devices such as in-vehicle, media phone, netbooks, and connected TV.