From what I've read on here, the reservations are open now but for some reason haven't been loaded up on the website. People have been able to call to book the reservation though!
Here is a tip for booking Fantasmic for January online: Don't use the drop down calendar to select your date. Instead, manually key in the date you want in this format: 01/02/2013 (or whatever date you want) and the availability will come up.