Microsoft also announced Data Sense, which helps users manage their smartphone data usage. Belfiore said the app had helped testers get 45 percent more Web browsing before hitting their data limit with the feature switched on.
To work, the feature needs carrier support. Verizon will be the first carrier in the United States to support it. Other carrier partners were not announced.
A similar tile-based home screen was used by Microsoft on Windows Phone 7, the predecessor to Windows Phone 8, but it didn't have the live updating feature.
The previous operating system succeeded in roughly doubling Microsoft's market share but failed to prove a hit with consumers. With the new software, Microsoft has put a lot more effort into polishing the user experience and attracting major phone makers to the platform, so greater success is expected.
The sale of the phones will signal the start of a showdown the size of which hasn't been seen in the mobile market for years. The new Windows handsets will compete against Apple's iOS and recently launched iPhone 5, which is the most popular smartphone, and also will compete with the fast-growing number of handsets based on Google's Android operating system, the most popular smartphone operating system.
Analysts believe the software will propel Microsoft into the No. 3 position as early as next year, when Windows Phone-based smartphones are expected to make up 6.6 percent of the smartphone market compared to 1.8 percent last year, according to IDC. By 2016, Microsoft will enjoy a 14.2 percent share, trailing Apple at 21.2 percent and Android at 58.6 percent, predicted IDC.
Attracting a large number of developers is key. Microsoft has been making an SDK available to some under a program, but Belfiore said the software company will on Tuesday announce a freely available SDK for the platform. The announcement is due to be made at its Build conference.
Martyn Williams covers mobile telecoms, Silicon Valley and general technology breaking news for The IDG News Service. Follow Martyn on Twitter at @martyn_williams. Martyn's e-mail address is firstname.lastname@example.org