These vacations are just too important for something to get screwed up. I always call, about three months and again, a few weeks ahead of time to confirm the ressie. It doesn't hurt, the MS people don't seem to mind at all. I call after their lunch or very early on a Wed or Thurs, never on Monday because they are mobbed for people trying to make ressies for the 12 and 7 month window on Sat, Sun and Monday.