在另一个Datagrid的RowDetailsTemplate中使用Datagrid

I would like to use a DataGrid within the RowDetailsTempalte of another Datagrid. This inner Datagrid should have its columns bound to a property of the current object in the outer Datagrid. For example, if the outer Datagrid is displaying all contacts by first name and last name, if I select a row I should be able to see another Datagrid containing all phone numbers associated with that contact. What I am most interested in is how the data of the inner Datagrid binds to the data of the outer Datagrid. Here is some XAML that I have so far to start with:I would like to use a DataGrid within the RowDe