public MainPage()
{
InitializeComponent();
txtPanno.TextChanged += txtPanno_TextChanged;
}
void TxtPanno_TextChanged(object sender, TextChangedEventArgs e)
{
TxtPanno.Text = txtPanno.Text.ToUpper();
TxtPanno.SelectionStart = TxtPanno.Text.Length;
}This code snippet for how to Type Uppercase String in windows phone TextBox WPF C#.