My experience this morning ended up being very positive.
We have a booking from Canberra to Cairns in mid Oct, on the direct flight, using points in J. I received an email to say there were flights changes (the direct flight has been dropped and now going via Brisbane), but the trip up was now going to take 9 hours, due to a 5 hour stopover in Brisbane. I rang at 9am and after 5 minutes on hold got put through to Vanessa (who by her accent I guess was in Fiji).
I had already looked up the flights and had an earlier flight from Canberra, linking through Brisbane and onto Cairns, with available points seats in J. She couldn't see that in her system, but I gave her the flight numbers and she managed to get us onto those flights. Vanessa did have to put me on hold a couple of times while she chased up other people to get the flights confirmed, and I could see it update on my bookings page, so I knew they had gone through. Vanessa apologised for it taking so long, but she did a good job as she followed it right through to make sure everything was ok. All up I was on the phone for 30 minutes.
I think the advice of others in having the alternative flight numbers available is helpful for the agents. There are obviously some steps that the overseas call centres can't do automatically, but in this case it all worked ok.