News about Microsoft's Windows Phone 7 update, Mango, has been building for a while now. But, at a developer conference in Japan, Microsoft CEO Steve Ballmer gave an actual number for the features expected in the pending update: 500.

Ballmer didn't offer up many details -- those will be revealed tomorrow at the launch event in New York -- but new handsets, new tools and (maybe) even a Skype app are likely on their way.

"We have a release that will come to market later this year -- not only is it a new release that is much more global, but we've added over 500 new features to Windows Phone," said Ballmer. "That information will be forthcoming, including some of the particulars about who is going to be building Windows Phone and which carriers will be offering them in Japan."

Mango also is expected to include the ability to make homescreen "tiles" out of any application feature or page.

"We're pushing for a different approach to user interface design, an approach which -- literally right on the homescreen of the Windows Phone -- you, our developers, can provide integrated experiences across your own and third-party applications that are alive and vibrant and real time for our joint customers," said Ballmer.

Other expected features include Internet Explorer 9, the Angry Birds app (the release has been pushed back to June 29), and a host of productivity-enhancing business tools.

Ballmer also addressed Microsoft's $8.5 billion acquisition of Skype.

"Skype is the most popular software on the planet for people who want to do real-time video connections," he said. "And we want to connect that up for business and consumer to all parts of the planet and continue to transform the future of communication."

Microsoft has a ways to go in its bid to compete with other smartphones on the market. A recent report from research firm Gartner revealed that Microsoft sold only 1.6 million phones in Q1 of 2011, in contrast to the 16.24 million iPhones Apple sold in the first quarter of 2011 (its holiday quarter). Google has said it activates nearly 400,000 Android devices each day, and has activated over 100 million smartphones to date.