Nature of Writing

Let me present some of the problems in which I am interested: What was the nature of writing before the emergence of the 'phonetic alphabet' (I've seen McLuhan using this term for the first time)? With the emergence of the 'phonetic alphabet' has language undergone any major change in the mediational role it is supposed to play in communication? If you say that even after the emergence of the 'phonetic alphabet' language continues to play the role that it had played earlier, then it should be inferred that 'writing' is only an activity that supplements speech.