You MUST call exactly 90 days before the date you want to dine at the Castle for breakfast. And, you MUST start calling a couple of minutes before WDW Dining opens (7 AM, on all days including weekends and holidays. All times are US EASTERN).
There are two possible greetings:
a) Thank you for calling the Disney Reservation Center. Our office is closed... (hang up immediately as soon as you hear the words "Our office" and hit redial immediately).
OR
b) Thank you for calling the Disney reservation center (pause). You're in and on hold! Wait! Do NOT hang up or you will lose any chance of a ressie!
Please note that as of October 2003, there is now a series of questions being asked. There is no way around them so listen carefully and press the buttons in response to each question.
Upon speaking to a "live person", interrupt the lucky CM and blurt out "I need Cindy's, for June xx, for x people, any available time". The CRO rep will understand your temporary rudeness, and you'll make up for it later with endless amounts of gratitude... Don't try and pick a specific time. Any delays will seriously hinder your ability to get a PS.
Use the 407-WDW-DINE (939-3463) number to directly call WDW Dining so you don't get caught in a transfer cue from CRO. This can amount to up to a 12 second delay in getting to Dining.
You will also need a credit card and there is now a cancellation policy. For more information, click here: New Cinderella's Royal Table Breakfast PS Policy
Source:
http://www.allearsnet.com/din/reserv.htm