>Also reading timing is just as subtle skill as reading faces.
I understand people "read timing" and interpret it as adding to the conversation but timing in a text conversation is so unreliable I personally give it no importance. More often than not the timing of my IM/text/email has more to do with the situation I'm currently in rather than how I feel about the conversation. I didn't reply to that last text because I just stepped into a meeting, or started driving, or got in the shower, etc.
An no, my reply can't wait because I had a tempo of conversation, and the person on the other side of the phone can't see that someone interrupted me in person. Face to face conversations transmit out-of-band information through body language, and in the same way electronic conversations transmit out-of-band information through timing. Also reading timing is just as subtle skill as reading faces.