Another important dimension is real-time communication vs slower communication. If it only takes a few seconds from saying something to hearing the interlocutor's reply, it's much easier to (say) assess inferential distances than if it takes several days. On this axis an IM chat is much like a meatspace conversation and a video message is much like a letter.

BTW, while you can't use intonation and body language in writing, you can use punctuation, formatting, and/or emoticons.