The big theme at Microsoft's MIX10 developer conference today was developing for Windows Phone 7 Series, and key to this was the new Silverlight 4. For the first time, Microsoft showed off third-party applications for the forthcoming phone platform, and talked about how third-party applications integrate with the platform.

Silverlight is becoming increasingly widely available for the browser, with Microsoft claiming 60 percent of all Internet devices now support it (up from 45 percent in October last year). The new version, available as a Release Candidate today with a final version next month, boasts new features to make it more useful for developing both in-browser and standalone applications, including support for microphones and webcams, printing, and the clipboard.

Silverlight 4 is of pivotal importance to Windows Phone 7 Series development. Windows Phones will not just run something like Silverlight 4—they will run Silverlight 4, exactly the same as desktops do. Likewise, for games, developers will be able to use the same XNA development tools that they can already use to create Windows and Xbox360 games, allowing deployment on Windows Phone 7 Series devices with minimal changes. Both Silverlight 4 and XNA will be fully hardware-accelerated on Windows Phone 7 Series phones, so Silverlight applications will have smooth scrolling and transitions, and XNA games will support proper 3D environments of the kind already familiar to PC and Xbox gamers.

Making Windows Phone use Silverlight means that the tens of thousands of existing Silverlight developers automatically have the capabilities to develop Windows Phone applications, using the concepts and software already familiar to them. This is in significant contrast to Windows Mobile development; Windows Mobile used a cut-down version of the Windows API, and .NET on Windows Mobile was similarly cut-down. For Windows Phone 7 Series, there's no cutting down. It's the same software environment. The utility of Silverlight 4 is set to grow; Redmond recently announced Silverlight for Symbian, and Microsoft has also signed an agreement with Intel to commit to delivering Silverlight on Intel's Moblin. This in turn should, eventually, allow those other platforms to be targeted as well.

Little was shown of the Windows Phone platform that wasn't previously revealed last month at Mobile World Congress. The major design points—the tiles on the Start screen, the use of the sideways scrolling/panning metaphor to drill down into data, and the use of various hubs to organize and consolidate data—had already been demonstrated. Finer details of the user interaction were described in more detail. For example, throughout the interface a heart motif is used for setting and removing favorite status, a normal heart to make something a favorite, a broken heart to revoke that status. This is used extensively; to remove a tile from the Start screen, you click its broken heart and it disappears.

Similarly, applications can have an App Bar at the bottom of the screen to provide direct access to common tasks, and, by expanding the App Bar, access to less common features. This will provide consistent access to features in a way that's more accessible than Windows Mobile's use of menus.

It's the apps, stupid!

In keeping with MIX's status as a developer convention, what we learned most about today was how applications can integrate with the OS, the tools used to do this development, and how applications can achieve the same look and feel as the OS itself.

Application authors will have few restrictions on the appearance of their applications. The development environment provides all the tools to create applications that look like the OS for those tasks where this is appropriate, but it won't be compulsory. Most of the Silverlight demos, such as a news reading application from the AP and a Windows Phone version of Shazam, did indeed retain the platform look and feel, using the sideways scrolling "Panoramic" concept and slick transitions between screens. A few apps, however, opted to break with the conventions entirely. A diary/journal application was shown off, which opted for a paper-like representation (complete with animated page turning).

Applications can integrate into the existing hubs, so that they're readily accessible from the place that makes most sense, rather than just in a big long list (as is the case in the current Windows Mobile and the iPhone). For example, image-manipulation programs were launched from and accessed through the pictures hub, and Shazam was part of the Music + Video hub. This means that even with third-party applications, the data hubs are still the primary front-end to user data; users don't have to learn new ways to access their data from applications—instead, it's a seamless experience.

Push notifications were also demonstrated, allowing applications to register for notifications that are delivered even if the application isn't running—clicking a notification will start the application. The actual notifications are routed through a Microsoft notification service that will provide all such notifications, and will be free to developers to use.

Monetizing applications is important to many. The AP application included ads (a rather offensive, full-screen ad in which a car drove over the content, creating a user experience as annoying as is common on the Web), and applications sold through Microsoft's Marketplace will be able to offer trial modes, without requiring the development of separate versions. A range of options were described; a trial might be time-limited, or disable certain features, or (in a game) only allow access to the first few levels. This provides a try-before-you-buy capability not presently available for the iPhone. One model not supported, at least initially, is in-application commerce. Games won't be able to offer downloadable content, for example, though Microsoft recognizes the value of this and a future version of the platform should include such a capability.

Key questions remained unanswered: we still don't know what multitasking, if any, will be available to third-party applications, and though the company says that Marketplace will be the one way to make applications available to end users, there should be some (as-yet undisclosed) way for organizations to offer applications internally to a limited user set. Backwards compatibility with Windows Mobile will be nonexistent, but there's a twist; because Silverlight 4 is compatible with Silverlight 3, developers will be able to use existing Silverlight code. And in fact, the first release of Windows Phone 7 Series will be using an extended Silverlight 3 (with additional features to allow the use of phone hardware like accelerometers), with full Silverlight 4 in a future version.

The company also reiterated that there will be no access to native code development, consistent with previously leaked documentation. Silverlight and XNA are the only options for application developers. This poses an interesting issue for Adobe: Microsoft confirmed that the company has no fundamental problem with the idea of a Flash runtime on Windows Phone, but for Adobe do to this, it would have to develop its Flash virtual machine to run on Microsoft's Silverlight virtual machine. This seems unappealing, and it's unclear exactly how Adobe will respond.

The development environment has three applications; the Visual Studio 2010 for Windows Phone Silverlight development environment, the Expression Blend 4 for Windows Phone design tool, and the XNA Studio 4.0 for Windows Phone game development environment. All are freely available, both now (in their beta and release candidate forms) and in the future. Developing for Windows Phone will always be free. The pre-releases are available to download right now.

The development tools look good. They all contain a full emulator for Windows Phone; this is no mere simulator, but the full Windows Phone operating system running within a virtual machine. Applications can be deployed and debugged either in the emulator or over USB to an attached Windows Phone. The emulator is fully featured; even multitouch is possible as long as it's being run on a Windows 7 PC with a multitouch screen. Though most applications being demonstrated were run on real phone hardware, a few applications used the emulator, and it provided an authentic alternative.

Overall, Windows Phone 7 Series is shaping up to be an attractive platform for both users and developers alike. High quality applications are a key part of the value proposition of smartphones, and though Windows Mobile has certainly had plenty of applications, their quality has been decidedly variable. From what's been shown so far, rich, capable, well-designed applications should be the norm for Windows Phone.