To the behaviorist, competence in the rules of language is not as important as the ability to speak it; speaking is what makes language real. Knowledge is a mental state and the structure of a language doesn t make it a language; it is the function of speaking words that makes a language a language.
Conversation is a form of interactive, spontaneous communication between two or more people. Typically it occurs in spoken communication, as written exchanges are usually not referred to as conversations. The development of conversational skills and etiquette is an important part of socialization.
Even sitting together in silence can be more communicative than a lengthy email, in some circumstances. Whether one is more important or less, is likely to be a function of what specific kind of communication is being undertaken, and in what specific kind of relationship.