Question: I often try to distinguish between immediate-feedback communication, such as talking in person, on the phone, or by instant message, and delayed-feedback communication, such as email. (Or at least, delayed in the sense that it's socially acceptable to not respond right away.)

I usually would say something like, "I'd prefer to discuss this in real-time," which usually gets the point across, but I'm wondering if there is a better way to describe this concept. ("Can we talk about this using an immediate-feedback medium?" sounds a little awkward.)

Answer: 
In pedagogical terms, we talk about "synchronous" vs. "asyncronous" communication.

In synchronous communication, we're talking to each other at the same time; in asynchronous communication, you may not see what I'm saying as I'm saying it, and you may reply at a later time.
Good question. In some ways, you are suggesting "active feedback" rather than passive, though that is not a common term and it doesn't mean "asap". 

Tech companies I have worked for also discuss a "positive handoff" which means reaching out to the person actively, such as via phone (I just emailed you the report) or in person (Here is the report) as opposed to a passive medium like email or a phone message. This is used for accountability purposes (I had a positive handoff of the contract with client X on 1/1/11, so he can't say he didn't know it was finished...)