Google on Monday released version 0.9 of the Android Software Development Kit (SDK), its open-source software stack for mobile phones.

Back in November, Google presented a preview version of Android to developers. The SDK has been updated three times since then. The new 0.9 SDK beta may not produce code that's fully compatible with devices running the final Android 1.0 software, but Android developer advocate Dan Morrill said in a blog post that "the APIs are now pretty stable and we don't expect any major changes."

Android apps are written in Java and run on Dalvik, an embedded virtual machine that operates atop a Linux kernel.

Google's effort to develop an open-source platform for mobile phone applications arises from its belief that mobile devices will offer stronger revenue opportunities than desktop computing in the years ahead.

To help make that belief a reality, Google last year formed the Open Handset Alliance, a group of more than 30 mobile operators, semiconductor companies, handset manufacturers, and software companies that is committed challenging telecom company control over network-connected devices.

The first Android phone, the HTC Dream, which will be offered by T-Mobile, just received approval from the FCC on Monday. T-Mobile is expected to being selling the phone before the end of the year, and perhaps as soon as the next few weeks.

Because there isn't yet an actual phone on which to run Android applications, the SDK includes phone emulation software for testing.

The 0.9 SDK features a number of changes, which are documented in the release notes. Among the most significant: the removal of the GTalkService instant messaging protocol, for security reasons, and removal of the Bluetooth API. Google is planning to re-introduce these services in a future release.

Android 0.9 features a new Home screen with a variety of user interface changes; new applications, including an Alarm Clock, Calculator, Camera, Music player, Picture viewer, and Messaging; and new development tools and APIs.

Further information can be found at the Android Web site.