Symbian source code is available for download now at http://developer.symbian.org/main/source/index.php
Whoever you are, you can look at the source and see how it works: You can experiment with it, you can try your own ideas and, most significantly, you can be part of the Symbian community.
All Symbian^3 platform source code is now available as open source code, to members and non-members alike, mostly under the Eclipse public license (EPL) but in part under other fully open source licenses.
The majority of the tool chain code is also now open and available under the EPL (or other open source licenses). There are just a few tools packages that have yet to complete their transition to distribution under the EPL, which will happen during the first half of 2010.