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Looking for a new smartphone? Your choice just got a substantially more complicated.

Monday, the first phones powered by the new Windows Phone 7 operating system hit store shelves. The new OS, the latest version of Microsoft's Windows Mobile software is effectively a fresh slate for the company -- a completely new operating system for smartphones.

Experts were cautious about how quickly consumers will adopt the new platform, but in general agreed that Windows Phone is an elegant offering.

"Windows Phone 7 is targeted as a consumer rather than a business OS," explained Sascha Segan, lead analyst of the smartphone team for PCMag.com. "It has great entertainment and gaming experiences, and it's highly controlled and curated."

Ross Rubin, director of industry analysis for market-research firm NPD Data, was more reserved, but believes that the new operating system is a big leap over old versions of Microsoft's mobile platform.

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"Microsoft has addressed nearly all the ills of the old Windows Mobile," Rubin told FoxNews.com, noting that the company was "starting over again" to address the gap between applications and features on other operating systems. "Long term, it will come down to carrier support and the momentum of other Microsoft properties and services integrated into Windows Phone 7 such as Office, Windows Live, XBox Live and Bing."

Those connections could be what makes the first crop of phones a hit -- and why Google will be watching Microsoft's moves closely.

"It sounds a lot like Apple's iOS ... which means it's most of all a threat to Android," Segan told FoxNews.com. "Apple has an installed base, committed developers and a brand halo that protect it for now. But WP7 will convert some potential Android buyers with its promise of a cleaner, more focused experience, especially with its Zune and Xbox components."

On Monday, the Samsung Focus hits AT&T stores for $200 with a two-year contract requirement. It will be closely followed by two more phones for AT&T, made by LG Electronics and HTC, and one for T-Mobile, also made by HTC.

From a hardware standpoint, the Windows 7 phones are indistinguishable from high-end Android phones: They have big touch screens, and a few models have slide-out keyboards.

In all, five Microsoft phones hit the U.S. market on Monday, including one from Dell, and it has lined up 60 carriers in 30 countries to carry Windows Phone 7. Early in 2011, the company will unveil three AT&T phones and two for T-Mobile and Sprint, Segan pointed out.

But Microsoft faces an uphill battle, Rubin noted, telling FoxNews.com that there won't be a big uptick in sales this holiday season, despite Microsoft's advertising push.

"In general, we don't see a lot of Q4 seasonal lift in the handset market. We tend to see more of a shift to mass merchant distribution in Q4; so Best Buy may help," he said.

In the most recent quarter, Microsoft's older system, Windows Mobile, accounted for just 5 percent of the worldwide smart phone market. That compares with 41 percent for Symbian (mainly used by Nokia), 18 percent for Research in Motion Ltd.'s BlackBerry phones, 17 percent for Android and 14 percent for the iPhone, according to research firm Gartner Inc.

"As RIM and Android handsets have seen, it is difficult competing with the iPhone at AT&T," Rubin noted.

To stand out from the competition, Microsoft has given the software has a different look. It is partly based on the aesthetic from the company's Zune media players. It is centered around "tiles" on the front screen that are supposed to tell the user at a glance about important new information, such as e-mail and Facebook status update.

For example, a weather program might show a constantly updated snapshot of weather conditions; photo or music libraries would be represented by a recent snapshot or the cover of the last album played on the device.

Both the iPhone and Android are fundamentally more application-centered -- the user has to tap on an application to see new information. However, some companies including Motorola Inc. have designed overlay software for Android that's reminiscent of Windows Phone 7's information-at-glance idea.

"We want you to get in, get out and back to your life," Microsoft CEO Steven Ballmer said at an event in New York. He called it "a very different kind of phone."

The software is designed to work well with Microsoft's cash-cow Office applications and to connect to Xbox Live, the company's online game service. Early word was that Windows Phone 7 would not support copying and pasting of text, but Microsoft announced Monday that the feature would be introduced through a software update early next year.

The Associated Press contributed to this report.

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