Microsoft has given software developers a lot to think about with Windows Phone 7. And at the company's yearly MIX conference this week, a lot of them were doing just that.

MIX focuses mainly on the Microsoft web platform, but Microsoft used it this year to go into much more detail about creating software for its radically redesigned mobile operating system. Based on conversations, most of the attendees looking at Windows Phone 7 are impressed with the new visual "face" of the operating system.

Some will plunge at once into Windows Phone 7 development, leveraging the release of free Express editions of the core Microsoft development tools, all now enabled for Windows Phone. Others, in both Microsoft and non-Microsoft development shops, have a more complex set of decisions to make. The fact that they're thinking about the decision at all is a victory for Microsoft's mobile ambitions.

Not all of these are enterprise-based or enterprise-focused developers. But their assessments and questions often reflect the same concerns and requirements of those who are. Their questions are part of the unfolding exploration of just what Microsoft is delivering, and not delivering, in the first release of the mobile platform.

On Monday, Microsoft announced that free Express versions of the latest iterations of its core development toolkits, enabled for Windows Phone applications, are available for download.

MIX10 attendees generally seemed impressed, even amazed, at what Microsoft achieved in the new UI layer for the mobile operating system.

"It's very new, and very nice," says Thomas Ribreau, project manager for Ave!Comics, an online marketplace for digital comics, based in Montpellier, France. "Microsoft has created a new way of to think [about mobile applications]. That's new to me, to see that in Microsoft."

The company evaluated Windows Mobile 6.5. "It was not smooth enough for us," Ribreau says. "The graphical functionalities were very very low." But Windows Phone 7 is causing Ribreau to rethink. "I think we can do something with it."

iPhone user Mark Tinderholt, a developer with Avanade, a systems integration joint-venture by Accenture and Microsoft, is struck by the Windows Phone 7's differentness from the iPhone UI. Avanade has done some big Windows Mobile deployments with a range of big private companies and public sector clients. One difference is Windows Phone's use of animation, movement and colour. "I had a visceral reaction to that," he says. "I just didn't like all the animation and movement. The iPhone is all column and row based. It's just different."

Another difference is the Windows Phone concept of "hubs." "It's very different from Apple," Tinderholt says. "The iPhone has discrete apps that do one thing. There's no integration." He has 35 applications on his own iPhone and he organises and administers them manually, with rather limited options. "Hubs integrate," he says. "They're a common place for similar activities. They give users a high level process or workflow view of the applications. It's more abstract. Whereas iPhone icons can be all over the place."

Both differences create opportunities for developers, Tinderholt says. But they also potentially create more complexity. "Windows Phone does open up opportunities for customisation. On the iPhone, you only have the [application] icon and you can set some indicators on it. Microsoft appears to be real flexible. But that creates a concern about it becoming a free-for-all."

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