I called this past Tuesday and was on hold for over 2 hours on my second attempt at getting through. The first call was disconnected after waiting about 40 minutes. It took over 200 times calling the second time to finally get through again.
We had a family suite at All Star Music booked for the first 10 nights in Dec, and they switched us to a suite at AoA at no extra cost to us. If we would have switched to a resort of our choosing (for us that would have been SSR or OKW), we would have had to pay the difference. This will be our first stay at AoA so hopefully we like it. Normally we stay on DVC rental points, so this was already going to be a much different trip for us. It does look like AoA has really good reviews.
As far as I know, if you wait and do not call to switch, Disney will cancel your reservation at 7 days before arrival date.