As far as grades are concerned, I think you just need a 2.0 and higher.
Interview tips:
The first interview round, is a web based interview. Its more like a personality test than anything else, and most companies now a days conducts them. They just want to evaluate to see if you are on time at work, a team player, you won't snap at difficult guests, and so forth. You are timed because Disney is looking for your gut response, be honest with yourself...don't lie! The first part of the test is just some senario questions, the second part is questions about your work and personal ethics. Try to answer most questions either in strongly agree or strongly disagree, from what I have seen and what I have did that seems to work. Do not get tripped up on their questions either, Disney will ask you the same question just reworded: "Are you always on time?" "Are you often late?" the same goes for "Are you a team player?" and "Do you like to work alone?"....you can't say yes to one and yes to the other, that shows you are inconsistant. Take the test as if you were already working for Disney World on your best day! It is really not that difficult.
Phone Interview:
I was a nervous wreck during my phone interview, but I smiled and answered everything confidently. Just smile (it changes the tone of your voice), be yourself, review the role checklist...I would suggest you go through the Tricky Interview Questions thread, there are a lot of helpful suggestions!
Hope this helps....good luck!