Windows Phone 7, Microsoft's new mobile operating system, passed a development milestone and reached the technical preview stage, the company said Sunday.

Microsoft is relying on the new operating system to rebuild its reputation in the mobile phone industry after a disappointing few years as Apple became the innovation leader with the iPhone and Google's Android mobile operating system emerged as a contender.

Microsoft recently killed a mobile phone called the Kin a month after the phone started selling.

Microsoft has said the new Windows Phone 7 handsets will start selling for the holiday season this year, but has not given a specific date.

"We are certainly not done yet – but the craftsmen (and women) of our team have signed off that our software is now ready for the hands-on everyday use of a broad set of consumers around the world...," wrote Terry Myerson in Microsoft's Windows Phone 7 blog.

The company is also sending prototype phones made by LG, Asus and Samsung to developers that want to build apps. The success of the Windows Phone 7 will depend, in part, on whether apps will be able to rival the array of apps available for iPhone users.

Update 12:42 p.m.:

Here is an extensive prototype review at Mobile Crunch that goes over several features: design, phone dialing, the touch-screen keyboard, the browser.