Google's ( GOOG) Android mobile phone operating system is rumored to be on a new Sony ( SNE) Ericsson ( ERIC) Xperia touchscreen phone due to be introduced later this year.

This would be the fourth major phone maker win for the Android system. It also would mark yet another loss for Microsoft ( MSFT) Windows Mobile software, which is quickly falling out of favor in a booming smartphone market. Motorola ( MOT), Samsung, HTC and now possibly Sony Ericsson are each working on Android phones that are expected to be available this year. There was even a rumor this week, which Nokia ( NOK) squashed, that speculated about possible Android-based phones in the works at the top phone shop.
Phone Ratings Index
Source: PhoneScoop

Android's invasion of the smartphone planet started last year when Deutsche Telekom's ( DT) T-Mobile introduced the HTC G1 phone. The lower cost, open-standard touchscreen device with slide-out keypad is designed to be a mobile Internet device.

Though it was exclusive to T-Moblie, the smallest national telco, and despite having a relatively unproven operating system, 1 million G1 phones were sold within the first six months of its debut.

The G1 has also earned strong reviews from its owners.

The G1 rates near the top of its 2008 smartphone class with a 4.2 score out of a possible 5, according to PhoneScoop's user review rankings. G1's closest peers Apple's ( AAPL) 3G iPhone and Research In Motion's ( RIMM) BlackBerry Curve 8330 scored 3.8 and 4.5, respectively.

The Android operating system is still considered the long shot in a race dominated by smartphone system leaders like Apple, Research In Motion and Nokia. But thanks to the fading popularity of Windows Mobile, Android's arrival could fit well in a market eager to find an independent smartphone operating system.

Google is already the dominant mobile search service, and Android's foothold in the smartphone software market is promising. Android now has a full-year jump on Microsoft, which has its wireless future riding on the release of its Windows 7 mobile software next year.