At one point in the novel, Jay Gatsby romantically describes Daisy as "the grail," alluding to the holy grail, the unattainable goal of the chivalric knights. In his quest for Daisy, whose name suggests purity, and in his romantic delusions, Gatsby perceives Daisy as the ultimate goal in his materialistic world. However, by saying that her "voice is full of money," Gatsby suggests that she is also like a material object, namely money, that can be attained.
Interestingly, this figure of speech that Gatsby employs is ironic. For one thing, Gatsby suggests that Daisy's speech is the language of the wealthy, when in reality she speaks of petty things, even foolishness. For another thing, it is not Daisy's voice at all that attracts Gatsby; it is the status of having a woman from the wealthy class that he desires. Rather than being prized for her voice and what she says, Daisy is merely a status symbol.
In reply to Nick's comment that Daisy has "an indiscreet voice" that is "full of --," Gatsby replies that "Her voice is full of money." By "indiscreet voice," Nick is referring to the fact that Daisy has spent all afternoon flirting with Gatsby and even telling him she loves him directly in front of her husband. Nick means that she lacks self-restraint and even wisdom. However, Gatsby's comment that "her mouth is full of money" refers to Daisy's wealthy upbringing and demeanor. As Nick further realizes, Daisy's voice sounds like the voice of a "king's daughter." She sounds self-assured and like she can obtain anything she desires. According to Nick, her voice even "jingles" and clinks like money. Gatsby is pointing out that it is Daisy's wealth that has allowed and driven her to behave the way she has, such as shamelessly and indiscreetly flirting with Gatsby in front of her husband, and Nick agrees.
Another interpretation of Gatsby's remark with regard to Daisy is that Daisy is a sort of material girl. Her voice being "full of money" is a symbol of what Daisy represents. She might not speak of money, but she certainly is attracted to the money. Evidence of this will be the fact that she marries Tom who buys her an insanely expensive pearl necklace after receiving Gatsby's letter.
Her "voice" also being a symbol of what Daisy represents suggests that she has always been with the wealthy. Daisy has always associated herself with wealthy people and it shows in the things she wears, the car she drove as a young girl (see Jordan Baker's narrative of Gatsby and Daisy's past)
One theme in The Great Gatsby is the idea of class inequality in America. Tom is of a higher status than George Wilson. So is Daisy. It is often thought that some people that have been born into wealth are not exactly intelligent, and this might be a representation of how ignorant Daisy is. After all, she does say a girl should be nothing but a beautiful fool. (Or something of the sort)
What it means:
Ex #1: Gatsby stops having the frivolous parties because Daisy does not like them, and "her voice is full of money" which means whatever she says is TRUE.
Ex #2: Daisy represents material wealth and all that comes with it. Such as class, beauty, comfort and power. Thus Gatsby is saying she is full of it. She has always had wealth and power, so it surrounds her.
*Note that this time frame was a time frame full of materialism in America, and individuals were following their dream- "American Dream."