Everything that's part of the core of Google's Android mobile operating system platform will be released under an open source license, according to ZDNet's Ed Burnette. Everything, he says -- including multimedia codecs, which are rarely shared.
Most will be released under version 2 of the Apache Software License (ASL), which Google favors and which is used by the Apache Tomcat and the Apache HTTP projects, among others. However, the parts of Android that have already been released under different open licenses will remain under their original licenses. For example, the Linux kernel enhancements in Android will be released under the GNU General Public License v2.
As for ASL v2, it doesn't require those who use Apache-released code in their software to also release those derivative works under the Apache license. They can choose to release them under another another open license or even choose to keep them closed source. In Burnette's words:
[I]t gives carriers, OEMs, and application developers the freedom to use whatever license they want for their own software. While Google encourages everyone to make their own code open if possible, it's not required by the license.
The fact that the core platform is open doesn't mean that the applications bundled with it will be open, too, however. Google's Gmail will remain closed, according to an employee quoted in the piece, because the company is "simply not ready to publish the API that talks to the back end server." That, of course, doesn't preclude Google from opening the API down the road.