I've only got one story, but it seems that I was able to get my request through MS when the regular dinning number said there was no availability. Last minute reservation (of course) trying to get dinner at Cali Grill on August 15 for 2 people. I was able to get a 5:45 pm reservation through WDW Dine but nothing later. I called MS about something else, and just for grins asked them about any openings. They were able to get me a 9:20 pm, which is what I really wanted. Woohoo. Now we'll see Wishes for DHs BD dinner....
BTW, the 800 number is nice...no long distance fee! That's a nice benefit.