There is no ListBox or anything in the DataTemplate for the ItemTemplate. For example, see the DataTemplate below:
<phone:longlistselector itemssource="{Binding DataCollection}" grid.row="0" xmlns:phone="#unknown">
<phone:longlistselector.itemtemplate>
<DataTemplate>
<StackPanel>
<StackPanel Orientation="Horizontal">
<TextBlock Text="{Binding Title}" Padding="5" />
<TextBlock Text="{Binding ImageSource}" Padding="5"/>
</StackPanel>
<ListBox ItemsSource="{Binding SubItems}">
<ListBox.ItemsPanel>
<ItemsPanelTemplate>
<StackPanel Orientation="Vertical"/>
</ItemsPanelTemplate>
</ListBox.ItemsPanel>
<ListBox.ItemTemplate>
<DataTemplate>
<TextBlock Text="{Binding SubItemTitle}" />
</DataTemplate>
</ListBox.ItemTemplate>
</ListBox>
</StackPanel>
</DataTemplate>
</phone:longlistselector.itemtemplate>
</phone:longlistselector>