Some of the page transitions in the user interface slide like the cards in Palm's Web OS.
The first version of Windows Phone 7 Series will not include Adobe Flash -- although Ballmer said he had "no objection" to Flash support. That marks the software apart from Apple's iPhone, which does not -- and will not -- support Flash.
Developers will have to wait until Microsoft's Mix conference in Las Vegas next month to learn whether Windows Phone 7 Series will support Microsoft's Silverlight in place of the missing Flash, said Microsoft spokesman Casey McGee after the launch presentation.
Microsoft plans to release a software development kit (SDK) to enable network operators and third parties to add new services and applications to the phones. AT&T, in the U.S., and Orange, in France, will be among the first operator partners to develop services specially for the phone.
Although the new software emphasizes functions rather than applications, and Microsoft intends to keep tight control of the user interface, it will be possible to download third-party applications and games certified by Microsoft through a "marketplace" hub. "There will be opportunities for partners to add value and build in functionality," said McGee.
Developers will have to wait to learn whether the applications they created for the previous version of Microsoft's mobile operating system, Windows Mobile 6.5, can be ported to the new platform, McGee said.
Microsoft's own mobile software developers are focusing very much on the new platform. "Windows Phone 7 Series is the priority for Microsoft's communications business," McGee said. Nevertheless, he said, the company will continue to deliver support for Windows Mobile 6.5 for three to five years from its October 2009 launch. He expects vendors to continue to launch devices based on Windows Mobile 6.5 for some time to come.
Microsoft expects the first phones running the software to be available by the end of the year, and says that network operators including Deutsche Telekom, Orange, Verizon and Vodafone, and vendors including Samsung, LG, Sony-Ericsson and long-time partner HTC have committed to offering devices running Windows Phone 7 Series.