Smartphones running Microsoft's (MSFT) new software are now available for AT&T (T) and T-Mobile USA customers.
The phones will compete with Apple's (AAPL) iPhone and an expanding number of phones with Google's (GOOG) Android system.
The first batch of handsets are made by Samsung Electronics (SSNLF) of Korea and HTC (HTCXF) of Taiwan.
Microsoft's older smart phone software lost market share against more modern competitors. Now, the company is starting fresh with Windows Phone 7.
Microsoft gave the software a different look from Android and the iPhone. It uses "tiles" on a front screen that provide users with things like email and Facebook updates at a glance.
More phones are expected soon, including one from Dell (DELL).
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