As an example, you could easily build the F# and C# Win Phone App (Silverlight) solution by doing the following:
1. Create a new C# Windows Phone Application (Silverlight).
2. Add a new F# Windows Phone Library project to the solution.
3. Add a new XML file to the F# project named MainPage.xaml.
4. Add content to the MainPage.xaml file as shown here (also change the Build Action option to Resource and the Copy to Output Directory option to Copy always).
5. Add the code from here to the File1.fs file.
6. Delete the MainPage.xaml and associated code-behind file from the C# project.
7. Change the App.xaml.cs code in the C# project to what is shown here (Note: You'll likely need to change the namespace).
8. Change the App.xaml code in the C# project to what is shown here (Note: You'll likely need to change the namespace).
9. Edit the properties of the C# project and change the Startup object drop down to the *.AppHost object.
10. Edit the WMAppManifest.xml file and change:
<DefaultTask Name ="_default" NavigationPage="MainPage.xaml"/>
<DefaultTask Name ="_default"/>
11. Finally, add a reference to the F# project, build, and test.