"To deliver what developers expect in the developer platform we've had to change how phone apps were written. One result of this is previous Windows mobile applications will not run on Windows Phone 7 Series," said Charlie Kindel, partner group programme manager for the Windows Phone application platform and developer experience at Microsoft, in a blog.
That's because with Windows Phone 7, Microsoft has decided to use Silverlight and XNA as development platforms.
Silverlight is Microsoft's multimedia runtime that competes with Adobe's Flash. XNA is the platform for developing games for the Xbox 360.
"If you are a Silverlight or XNA developer today you're gonna be really happy," Kindel said.
That appears to be true, judging from comments posted during and after a Twitter question-and-answer with the Windows Phone team at Microsoft about the news.
"Very good news for any #silverlight and #xna developer :)," Pawel Bojkowski, a developer, said in a tweet.
Johan van Mierlo, a Microsoft MVP for Windows Mobile Devices, also wrote that he approves of the change. "IMO this is all good!" he said on Twitter.
The move to Silverlight shouldn't be a big surprise for most developers. "Microsoft has always said, 'Learn Silverlight, it's an important development environment for the future,'" said Matt Rosoff, an analyst with Directions on Microsoft.
Plus, Microsoft hasn't really pushed its Windows Mobile 6.5 Marketplace very hard, he noted. That may have given developers a clue that changes were afoot.
Microsoft, however, says it isn't abandoning the Windows Mobile platform just yet.
"To be clear, we will continue to work with our partners to deliver new devices based on Windows Mobile 6.5 and will support those products for many years to come, so it's not as though one line ends as soon as the other begins," Kindel said.
What is still uncertain is whether any phones currently on the market will be upgradeable to Windows Phone 7.
Microsoft has been coy on that matter, presumably because it doesn't want to jeopardise sales of current-generation products between now and when Windows Phone 7 products hit shelves later this year.
During the Twitter question-and-answer, the Microsoft employees did not shed any light on the matter.
They mostly repeated the official response from the company, which is that it can't confirm if users will be able to upgrade from Windows Mobile 6.5.
They also repeated another vague statement about whether the HTC HD2 will be upgradeable.
"Currently we don't have plans to update the HTC HD2 to WP7," the Windows Phone 7 team said on Twitter.
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