I can't speak for other airlines but at the star we never have the INT on during pushback. A case could be argued after an incident like this that maybe we should have it switched on but as someone alluded to before; it ain't no engineer on the receiving end especially not if you're operating in NZ.
As for SOP, depends where you're operating. If you're in NZ then 9 times out of 10 it gets switched on as soon as the ground guy has disconnected but I'm lead to believe it's hardly used in Australia. Could be wrong but that's the general consensus.