Hi there, Kim!
What a great idea that is, and it will definitely generate a lot of excitement around your home before you head to the four Park of the Walt Disney World Resort!
You can
schedule the call in advance online.Just be sure that you read the
frequently asked questions; you'll need to know the calling-from number and the amount of time you'll have to answer before the automated system assumes you are not available.
There is a window of time provided - a margin of error, if you will - for the call to come in, so you want to factor that into your schedule, too.
Have a wonderful time, and enjoy the special greeting from your family's favorite Disney friends!
See you later, celebrator,
-Deborah B.