The iPhone MKMapView doesn’t include driving directions as far as I’m aware, but the default map app does. So what do you do when you want driving directions in your own app? The answer is pretty simple and works on v3 and v4. All you need to do is construct a Url for google maps and pass it to the map app:

                UIButton btnDirections = UIButton.FromType(UIButtonType.RoundedRect);
                btnDirections.Frame = new System.Drawing.RectangleF(160, 320, 150, 40);
                btnDirections.SetTitle("Directions...", UIControlState.Normal);
                btnDirections.TitleLabel.TextAlignment = UITextAlignment.Center;
                double slat = (double)appDelegate.myLocation.Coordinate.Latitude;
                double slng = (double)appDelegate.myLocation.Coordinate.Longitude;
                string saddr = slat.ToString() + "," + slng.ToString();
                string daddr = _fishery.FisheryLat.ToString() + "," + _fishery.FisheryLng.ToString();
                btnDirections.TouchDown += delegate {
                    NSUrl url = new NSUrl("http://maps.google.com/maps?saddr=" + saddr + "&daddr=" + daddr);
                    UIApplication.SharedApplication.OpenUrl(url);
                };
                this.View.AddSubview(btnDirections);