No you want to go through the Disneyland app or the Disney web site.
Always book through Disney my experiences app. If you have a account setup through them or you can go to walt disney.go on Google and use the system. Three bars on top left and then my disney dinning reservation, it will show you all the restaurants, click on the one you want then sign with your account and will tell available and time.
It's all done through the website or app. If you call, they will tell you that the reservation system is performed online. If you book a stay at the hotel, then you can book through the hotel.
I don’t know if you can use Open Table. I would assume you need to do it through Disney. We did a standby reservation on the same day and just got lucky to get in. It was worth it.
No, you must use the Disney website/app only. I wouldn't recommend trying to call
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