Amazon.com is expanding its digital music presence to the mobile realm by developing a version of its MP3 music store for Google's new Android mobile phone platform.

The first phone compatible with the Android operating system was announced today, the G1, offered by wireless operator T-Mobile. The Amazon MP3 store is one of many applications designed for the new software, and T-Mobile is supporting the service.

In a nutshell, the mobile version of the Amazon MP3 store allows G1 users to browse and search the Amazon digital music store and listen to 30-second song samples via the T-Mobile network. To buy and download a song, however, the phone must be in a Wi-Fi hotspot, similar to the iPhone's access to iTunes.

All the music purchased will be DRM-free, just like the rest of the Amazon catalog. No mention yet of whether the phone-purchased songs will be smaller or more compressed files than those purchased via the computer.

The Amazon store will be preloaded into the G1 device, and has the full blessing of T-Mobile - the only major U.S. operator previously without a full-song over-the-air music download service. In theory, any other Android-powered device could also either ship with or add the Amazon music application post-purchase, but whether the operator adding such a phone to its network allows users to do so remains to be seen.

The G1 phone is manufactured by HTC, based on its "Dream" model. The open platform that Android boasts allows users to download additional applications as they are created for the software, similar to the iPhone App Store. However, Google has promised to be far more flexible with the types of applications created than Apple is (Apple, for instance, does not give developers access to the iPod or iTunes functions of the device).

Further details, such as price and availability, will be unveiled at the official Android press conference later today.