Mary Jo Foley’s post speculating about Windows Mobile 7 coming in Q1 2009 says:

From recent executive remarks, it sounds like Microsoft is trying to get Windows and Windows Mobile to be more in sync.  Might this mean with Windows Mobile 8 — which Microsoft has told certain folks will be built from scratch — Microsoft might make Windows Mobile a “real” version of Windows, with the same core as Windows client?

I heard from someone at Microsoft probably 5 or 6 years ago that this was the plan.

Windows Mobile currently runs on top of Windows CE which essentially supports a subset of the full Win32, etc. APIs, so doing native (C++) development for Windows Mobile is similar to desktop development (just a little more ‘cramped’).  There is also the .NET Compact Framework, similarly a subset of the full .NET Framework.  There are also Windows Mobile specific APIs at the native and .net level.  Some of the internal sub-systems, for memory, processes, etc. are quite different.

To make Windows Mobile a ‘real’ version of Windows at the core is therefore a lot about how much Windows CE is API-wise (inc. .NET) and sub-system-wise, similar to the Vista kernel.  After that, we have the shell and applications.

The shell clearly cannot be Aero, and the UI experience expectations for mobile has been clearly set by the iPhone with everyone else playing catch-up.  The mobile device really needs a bigger or paper-like-expandable screen at some point – there’s only so far you can go with zooming.

Applications can be split between Office (and other productivity or line-of-business apps) and all the other software+services things that are required activities in this era.  No doubt Windows Live pieces need to be upgraded and combined with great UI.

Why not make Windows Mobile a .NET-only platform with WPF for the shell with add-ins for all MS and 3rd-party applications?  The mobile space is not big enough that breaking compatibility is such a big deal.  It truly can’t be long before Microsoft partners with nVidia and produces a Microsoft ‘mPhone’.  An investment in small WPF mobile versions of Office would be a re-usable investment allowing for web based Office running on Silverlight!