It's tough to tell from the defense motion, but let's think about which parts of which 911 calls they actually want to exclude.
CALL #1: Nothing much here, except maybe the conversation between Cindy and Casey while on hold--Cindy threatening to take custody, Casey asking for "one more day." None of this is hearsay, because Cindy's statements would not be offered to prove the "truth of the matter asserted" and Casey's statements are statements of the defendant.
CALL #2:
Operator: Is Casey not telling you where her daughter is?
Cindy: Correct.
OK. So Cindy's (implied) statement here is: "Casey will not tell me where Caylee is." This is a statement that was made out of court by Cindy and would be offered to prove the truth of the matter asserted (that Casey would not tell where Caylee was). This is a relatively calm call and includes all the silliness about the stolen car and money, so the statement might not qualify as an "excited utterance." It might qualify as a spontaneous statement describing a condition or event while the person (Cindy) was then perceiving the condition (Casey's refusal to tell where Caylee was). But even if the statement is initially excluded as hearsay, if Cindy lies about it on the stand it will come in under a hearsay exclusion for prior inconsistent statements of a witness.
CALL #3: We all know this is the one the defense is worried about.
Cindy (crying): ...Her, her mother finally admitted that she's been missing.
...
Cindy: ...[M]y daughter finally admitted that the babysitter stole her. ...
...
Cindy: ...
he just admitted to me that she's been trying to find her herself. There's something wrong. I found my daughter's car today and it smells like there's been a dead body in the damn car.
...
Cindy: ...I'm scared (unintelligible--crying hysterically). Caylee's missing. Casey has admitted Zanny took her a month ago. She's been missing for a month.
...
Operator [to Casey]: Can you tell me a little bit what's going on?
Casey (calm): My daughter's been missing for the last thirty-one days. ...
Operator: And that you know who has her?
Casey: I know who has her. I've tried to contact her. I actually received a phone call today now from a number that is no longer in service. I did get to speak to my daughter for about a moment, about a minute.
...
Operator: And you last saw her a month ago?
Casey: Thirty-one days. It's been thirty-one days.
Operator: Who has her? Do you, do you have a name?
Casey: Her name is Zenaida Fernandez-Gonzalez.
Operator: Who is that? Babysitter?
Casey: She's, she's been my nanny for about a year and a half, almost two years.
Operator: And why, why are you calling now? Why didn't you call thirty-one days ago?
Casey: I have been looking for her and have gone through other resources to try to find her, which was stupid. But...
OK, the statements from Casey are easy. Non-hearsay because (1) statements of the defendant, and (2) not offered to prove the truth of the matters asserted (i.e., the State will not be trying to prove that ZFG stole Caylee, or that Casey got a call from Caylee on July 15. Quite to the contrary.).
How about Cindy's statements? First of all, every bit of Cindy's part of this call would fall within the excited utterance exception IMO. This is like a law school exam example of an excited utterance. Notice that Cindy has dropped all attempts in this call to give some fake reason for the detectives to come--the car, the money--because she has finally realized that an actual emergency exists: Caylee is not just being hidden from Cindy but is actually MISSING. This puts the smell in the trunk in a whole new (terrifying) light for Cindy.
Second, if Cindy is inclined to lie about any of these things (i.e., if she denies that she believed that the car smelled like a dead body) then those parts of the call will come in to impeach her.