Google's Android operating system is expected to capture 4% of the U.S. smartphone market during the fourth quarter of 2008, according to research group Strategy Analytics.

The estimate comes as the first Android handset, tentatively known as the Dream, is set to be unveiled Sept. 23 by T-Mobile. Although the details aren't confirmed, FCC filings show the HTC handset will have a large touch screen that flips out to reveal a QWERTY keyboard, Wi-Fi, and Bluetooth capabilities.

Strategy Analytics said 10.5 million smartphones will be sold in the United States during the fiscal fourth quarter, and the Android smartphone will sell 400,000 units during that time frame. By comparison, Apple's iPhone 3G sold 1 million units worldwide in its launch weekend, with industry analysts estimating the majority of those sales were in the U.S. market.

"Android is a relative late entrant and it will join an increasingly crowded market alongside BlackBerry, Microsoft, Apple, Palm, Symbian, and LiMo," said Neil Mawston, Strategy Analytics' director of wireless device strategies, in a statement.

Google's brand will be a strong driver of adoption, the research group said, but the biggest issue will be the carrier subsidy. Part of the latest iPhone's success is because of the relatively inexpensive price point, and The Wall Street Journal said the first Android handset is expected to debut for $199.

"Longer-term success will, of course, rest on Android vendor ability to create designs with wow factor and an intuitive user-interface," said Chris Ambrosio, Strategy Analytics' executive director, in a statement. "Google will do its part to drive growth, and we expect Android will eventually offer a compelling range of mobile applications emphasizing Google's online assets, such as advertising, mapping and search."

While sales comparisons of the Dream and iPhone 3G are inevitable, Android is expected to be a on a slate of different handsets in the coming years, with one expected from Sprint in the first half of 2009.