Okay, the policy changes on 10/27/09. Here are the rules (plus or minus a day)...you should figure out the exact math yourself:

If you arrive at WDW prior to 1/25/10, then you are on the 90 day plan. Take your arrival date and back up 90 days.

If you arrive at WDW between 1/25/10 and 4/25/10, you need to call on 10/27/09, as everybody in that group is within 180 days of 10/27/09 and that's when the new rule takes affect.

If you arrive at WDW after 4/25/10, then count back 180 days from your arrival date.

Unless, of course, they change the rules again.