Visit your friendly Volkswagen dealer... :-)
You need to purchase Voice Control from Volkswagen - it is an Activation Code that the dealer needs to input.
When purchasing our GTI we made sure we optioned it at no cost - it had to be ordered in from Germany and took a few weeks. I've heard some dealers charge between $250 and $450 for this. You may be lucky if you have a good relationship with your dealer to get if for no charge, but don't count on it.