How to set the links in a text block clickable in wp7
<TextBlock>
    <Run>Pure Text</Run>
    <HyperLink Command="{Binding HyperLinkTapped}">http://google.com</HyperLink>
    <Run>Pure Text Again</Run>
</TextBlock>

private void OnMessageReceived(string message)
{
    var textBlock = new RichTextBox()
    {
        TextWrapping = TextWrapping.Wrap,
        IsReadOnly = true,
    };

    var paragraph = new Paragraph();

    var runs = new List<Inline>();

    foreach (var word in message.Split(' '))
    {
        Uri uri;

        if (Uri.TryCreate(word, UriKind.Absolute, out uri) ||
           (word.StartsWith("www.") && Uri.TryCreate("http://" + word, UriKind.Absolute, out uri)))
        {
            var link = new Hyperlink();
            link.Inlines.Add(new Run() { Text = word });
            link.Click += (sender, e) =>
            {
                var hyperLink = (sender as Hyperlink);
                new WebBrowserTask() { Uri = uri }.Show();
            };

            runs.Add(link);
        }
        else
        {
            runs.Add(new Run() { Text = word });
        }

        runs.Add(new Run() { Text = " "});
    }

    foreach (var run in runs)
        paragraph.Inlines.Add(run);

    textBlock.Blocks.Add(paragraph);

    MessagesListBox.Children.Add(textBlock);
    MessagesListBox.UpdateLayout();
}