Appforge has announced the beta test of Appforge Crossfire. This is the system that allows .NET development across multiple platforms. AppForge Crossfire will enable mobile development with Visual Studio .NET. You can apply for the beta program here.

Info from Appforge website:
AppForge Crossfire Beta Tester Application
If you are interested in developing applications using AppForge Crossfire and Microsoft Visual Studio .NET for Palm, Symbian, Pocket PC, and Nokia Series 60 devices, (or other mobile and wireless smartphones and devices) and would like to be considered as a beta tester for future product releases from AppForge, please complete the following survey.

Please note:
- This beta sign up is an application only. There is no guarantee that you will be accepted in the Beta Program.
- Those accepted will receive pre-release AppForge Crossfire software. There is no additional compensation for participating in the Beta Program. There are no free licenses or free upgrades of the full release version of Crossfire for Beta participants.
- Microsoft Visual Studio .NET 2003 is required.
- Due to the large volume of applicants, only those individuals who have been selected will be contacted. We thank you for your interest in Crossfire.