Clearly, conversation is crucial to Holden and his character's development. Look at the very structure of the novel. Holden't starts the novel out as a conversation between himself and the reader. Pivotal moments of the novel occur through conversation. Before leaving school, Holden goes to discuss his situation with his teacher. He calls Sally up and asks her to meet him so they can talk. He goes to the house of a former teacher to talk. Consider then all the situations in which he doesn't talk--after Allie dies, alone in his hotel room in the city, and myriad others. Holden's subconscious realization is that talk is important to his healing.
Enotes has some great resources for further research.