Is it OK to fire someone by txt?

Thinking of affordances again, and which affordances fit best with which contexts...

In a discussion forum on the relative affordances on chat and asynchronous communication, the following question arose:

"Is it possible to step back and, on the basis of your experience, think of contexts (or types of context) in which the affordance of either synchronous or asynchronous communication would strongly influence which one you would use?"

I am thinking, for instance, of the practice that seems to be creeping in of firing people by txt or email. Email maybe, although it would have to be a context in which even a phone call was impossible. Txt? I cant think of any context in which txt would be appropriate.

Question: Is 'appropriate' different from 'affordance', and if so how?