How Can I Make A Call In Windows Phone 8 App.?

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C#

Windows-Phone-8

i am using the code

private void image1_Tap_1(object sender, System.Windows.Input.GestureEventArgs e)
        {
            PhoneCallTask task1 = new PhoneCallTask();
            task1.DisplayName = "Fire Brigade";
            task1.PhoneNumber = "102";
            task1.Show();
        }

But it gives an exception "An unhandled exception of type 'System.UnauthorizedAccessException' occurred in System.Windows.ni.dll"

Any suggestions on how to make it work.?