It is usually considered that a writer has much more time to formulate his thoughts, to re-write, to edit, etc. than a speaker does; however, during an e-chat conversation each interlocutor (although both of them write, not speak) faces almost the same time constraints as a participant of a spontaneous face-to-face conversation: an interlocutor must indeed simultaneously monitor what he and his collocutor say (by reading phrases on the screen, which, as a task, activates other neuroanatomic mechanisms) and plan his next utterance.
While conversation continues interlocutors in both types of conversation (i.e. oral spontaneous speech and e-chatting) are normally expected to keep talking without long interruptions (although written material is available for checking/returning for better comprehension in case of e-chatting) and in that respect e-chatting is of course closer to oral conversation than to writing.