"The static grid of icons has been the standard on smartphones," said Belfiore. "We decided not to use that tired old metaphor. Our way is to put people at the center of the experience."

People users interact with can be given their own tiles so that the latest interactions on email or social media are updated.

"It's the most personal smartphone operating system you can get and keeps you closer to the people that matter most in your life because of that," he said.

Belfiore announced a number of new apps that will be available for the platform including versions of Facebook, Twitter, Skype, Angry Birds, Urban Spoon and, from early 2013, the Internet music streaming service Pandora will be available. Windows Phone 8 customers will get a year-long free subscription to Pandora's ad-free service.

"We estimate 46 of the 50 most-used smartphone apps will be on Windows Phone 8," said Belfiore. "That's huge progress for us."