Although they are rare, there are a handful of exceptions to the 90 day rule. If you go to the main page at www.wdwinfo.com and look in the bottom left corner you will see the PS Calculator. It lists how many days out you can make PS's for every place at WDW. You can enter the date you're interested in, and it will tell you when to call.
Regarding Credit Cards...except for CRT, if you are asked for a credit card it's only to hold the PS time for you. Always ask about any cancellation policies if you give a CC#.
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