Telerik UI for Windows Phone by Progress

The RadPickerBox control expands or opens its popup when the user clicks on it. Additionally you can control the expanding and the collapsing of the RadListPicker control via its IsExpanded property.

CopyXAML
<telerikInput:RadListPicker x:Name="radListPicker" Header="Country:" VerticalAlignment="Top" IsExpanded="True"></telerikInput:RadListPicker>