Microsoft’s Charlie Kindel has blogged about the Windows Phone 7 development platform.

As widely leaked, the new mobile device supports Silverlight and XNA; Kindel also mentions .NET, but since both Silverlight and XNA are .NET platforms, that might not mean anything additional.

The big story is about compatibility:

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.

This puts Microsoft in an awkward position. Support for custom business apps has been one of the better aspects of Windows Mobile. What Microsoft should do is to have some way of continuing to run those old apps on the new devices. Instead, Kindel adds:

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.

I would not take much account of this. No doubt there will some devices, but demand for Windows Mobile will dive through the floor (if it has not already) once Phone 7 is available, making it an unattractive proposition for hardware partners.

The danger for Microsoft is that after this let-down, those with existing Windows Mobile apps that are now forced to choose a new development platform might choose one from a competitor.

The mitigation is that apps which use the Compact Framework will likely be easier to port to Windows Phone 7, because the language is the same. Native code apps are a different matter. Of course it will be technically possible to write native code apps for Windows Phone 7, but probably locked down and restricted to special cases, such as perhaps the Adobe Flash runtime (I am speculating here).

PS – I see that developer Thomas Amberg has articulated exactly these concerns in a comment to Kindel’s post:

Platform continuity was the single most important feature of Windows Mobile. Being able to run code from 2003 on a current phone is more important to our customers than a fancy UI (which Microsoft seems not able to get right anyway). Further, the ability to access hardware specific APIs through P/Invoke has been vital in many of our projects (e.g. to use Bluetooth in the early days). Those advantages have now gone. You just rendered useless years of development work and many thousands of lines of code.

"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"

You will, I bet. But which device manufacturer will produce such "dead-end" devices?

Time to switch to another mobile OS.