Microsoft introduces Windows Phone 7

Microsoft on Monday formally unveiled its Windows Phone 7 mobile operating system, which it hopes will give it a greater presence in the rapidly expanding market for smartphones.

Phones running the new software will be available on AT&T's network starting on Nov. 8, said Steven A. Ballmer, Microsoft's chief executive, at a news conference in New York.

Later in the year, the phones will be available from T-Mobile, and in 2011, from Verizon and Sprint. AT&T will initially offer three phones, at $200 each.

In all, the operating system will run on nine new phones, made by LG, Samsung, HTC and Dell, Mr. Ballmer said. Some will have keyboards, he said, while others will be exclusively touch screen.