The move was another step in concluding a Nokia initiative that didn't deliver all the benefits the company hoped for, according to analyst Roger Entner of Recon Analytics. While Symbian was made available as open source, a few handset makers, such as Samsung Electronics and Sony Ericsson, took advantage of the OS. But because Nokia was such a dominant maker of Symbian phones, the partner companies were never able to gain enough traction in the market to make it worth their while, Entner said. The situation became even less promising for them when Symbian was leapfrogged by Apple's iPhone, he added.

"Why go through the effort of providing it open source, when nobody's there?" Entner said.

The move may have been aimed at cutting the costs of managing Symbian, though there is a chance Nokia did it because it aims to come out with new features in Symbian that it wants to protect from competitors, said analyst Avi Greengart of Current Analysis.

Though Symbian was the biggest smartphone OS in the world last year, it has been losing ground to rivals and is expected to shed more soon. Last week, research company Gartner said Symbian held 37.2 percent of the smartphone market in 2010 but would fall to 19.2 percent this year and just 5.2 percent in 2012. Android would reach nearly 50 percent of the market by then, Gartner said.

The change in licensing will not have a significant effect on developers of applications that run on Symbian, because they don't need to get into the code or modify it, analysts said. In any case, app developers already have largely been drawn away by other OSes, Greengart said.