I heard, c#.net and QT can be mixed for mobile development. I shall like to share of your experience with the same.
Basically, we have c#.Net background and wish to reuse the skill/knowledge of these for expanding products into mobile platform. We have seen J2ME. But it needs specific skill/resource development. We shall prefer .Net for this. But Windows mobile is not having too much of footprint.
Shall like to have your inputs.
You can use two processes and communicate via say socket/shared memory. So it's possible to merge different codebase and deploy.
However if you are looking to target app stores etc. I suggest you stick to one language only. If you intend to make UI using QT then you would end up teaching yourself Qt Designer, SIGNAL SLOT Mechanism etc. I guess from there it's not a huge learning curve to make the entire app in Qt/C++.
Windows on Mobile has a very small footprint. If you want you app to target all app stores or more than you should try HTML5