Symbian is based on open source platform for mobile phones. But after the distribution of Android OS, many device makers such as Samsung and Sony Ericsson have been adopting Android OS instead of Symbian.
Nokia released the its decision that Symbian platform would be controlled by the company, while Symbian foundation will take care of only licensing of the software.
In the aspect of market share, Symbian is still the number one operating system with a 37% share in the 3rd quarter. And the market share of Android is 17%. But the decreasing trend of a market share is continuing and time comes that Nokia changes its long-preserving open system.