Quite unexpected Google released their source code of Android 4 (Ice Cream Sandwich)
Here's the announcement:
"Hi! We just released a bit of code we thought this group might be interested in. Over at our Android Open-Source Project git servers, the source code for Android version 4.0 (Ice Cream Sandwich) is now available."
"This release includes the full history of the Android source code tree, which naturally includes all the source code for the Honeycomb releases."
Head over here for the original posting.