Have to say that from our point of view that we would always prefer a call if there is to be a route change due to the fact that the AFTN Ack's are not usually checked - instead we use RCA to make sure they have gone in.
The problem arises if we send the plan off to the F/D with an unchanged route and it HAS been changed by yourselves.
This isn't to say that we dont appreciate your help just that we'd like a phone call.