Charlie Kindel recently blogged that Windows Phone 7 will officially not support Windows Mobile applications.
For us, the cost of going from good to great is a clean break from the past. To enable the fantastic user experiences you’ve seen in the Windows Phone 7 Series demos so far we’ve had to break from the past. 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.
However all is not lost for existing Windows Mobile developers as the Windows Phone 7 series device will support familiar technologies such as:
In any case more information about the entire development process for WinPhone 7 will be announced at MIX 2010 in less than a week. So stay tuned for more info…
Source: Charlie Kindel on Windows Phone Development : Different Means Better with the new Windows Phone Developer Experience