Google's posting of the Android 4.0 source code has led to an early port to the Nexus S for those willing to experiment. The custom-built firmware has most hardware and software features working, including 4.0-specific features like hardware acceleration of the interface and Face Unlock. A follow-up Wi-Fi patch is needed to get the shorter-ranged wireless working, but it can otherwise work as a full phone.
The unofficial install still carries significant risks. USB Mass Storage doesn't work, although ADB mode does. Video recording also doesn't work, and the Data Usage app can't track what's running. By its nature, the build doesn't include the bottom navigation buttons on the touchscreen and still relies on hardware controls.
Early testers can get the code for both the original, T-Mobile oriented Nexus S or the Nexus S 4G on Sprint. Either install is "at your own risk," forum member kwiboo warned, and risks problems. Officially, Google is due to push an official Android 4.0 build to every Nexus S in the next few weeks and will be the safest route.