gistfile1.cs

twilio.SendSmsMessageAsync("5551111111", "5552222222", "Async! ", (msg) => {
    Dispatcher.BeginInvoke(() => { txtOutput.Text = msg.Sid; });
});

twilio.SendSmsMessageAsync("5551111111", "5552222222", "Async! ", smsSent);
public void smsSent(SmsMessage msg) {
    Dispatcher.BeginInvoke(() => { txtOutput.Text = msg.Sid; });
}

// or

twilio.SendSmsMessageAsync("5551111111", "5552222222", "Async!");
twilio.SendSmsMessageCompleted += smsCompleted;

public void smsCompleted(object sender, SmsCompletedEventArgs e) {
    Dispatcher.BeginInvoke(() => { txtOutput.Text = e.Message.Sid; });
}

That looks awesome! I think I need to dig into Rx.........