You can change this behaviour slightly such that the first possible suggested word / sentence is filled in the AutoCompleteBox .
To do that Just set the IsTextCompletionEnabled property of the AutoCompleteBox to True.
Automatic text completion in AutoCompleteBox in Windows Phone
public partial class MainPage : PhoneApplicationPage { // Constructor public MainPage() { InitializeComponent(); AddAutocomplete(); } public void AddAutocomplete() { AutoCompleteBox txtbox = new AutoCompleteBox(); txtbox.IsTextCompletionEnabled = true; stack.Children.Add(txtbox); // Data txtbox.ItemsSource = GetSports(); } public List<string> GetSports() { List<string> Sports = new List<string>(); Sports.Add("Cricket - One Day"); Sports.Add("Cricket - Test"); Sports.Add("Tennis"); Sports.Add("Table Tennis"); Sports.Add("Hockey"); Sports.Add("Football"); return Sports; } }