The list view is like a table and it is simply displaying the content of the table. What you can do is to add the mobile field to the columns that you want the tree view to display. This is very easy. just locate the address tree view in the xml and add the mobile field to it (test with this) so for ever contact, you have the mobile and phone displayed. once this works you can build a module that inherits the address mobile and replace the mobile field using xml