Depending on where you want to eat, some reservations may be available now (on opentable.com). We're going in August as well, and already have ressies for dinner at Finnegan's (5:00), Mythos (4:30), Tchop chop (6:30), and Emeril's (12:00). There are a few restaurants in citywalk and the Luau that we're trying to get ressise for, and a pp is accurate, it seems as if you have to wait until 2 months prior for those. When I spoke to CS online, they told me that they do not take ressies until 30 days prior to your arrival for dining. I assume that they hold a number of "prime dining ressies" back from opentable (where we made all of ours so far) for those bookings, but that's just my opinion...not a verified fact. If I"m remembering what I've read correctly, you also have to call a different number for in-park ressies than you do for city walk ressies...
US restaurants: 407-224-FOOD (3613)
IOA restaurants: 407-224-4012
Citywalk: 407-224-FOOD (3613), but some restaurants, you have to call directly
Most hotel restaurants:407-503-DINE (3463), others, you may have to call directly
At least, this is what I've culled from my readings!! YMMV!