Well even though it was still in warranty when I sent it off, unfortunately Optus took a couple of weeks to decide that they don't fix that model anymore. I'm told that the company that does handle repairs wouldn't do it under warranty then...
So finally I rang out our IT department to find out what's going on, and they said that it is fixed. Great. Except that they said what fixed it was upgrading the firmware to the latest version. Hmm, hadn't I already done that a while ago? Skeptical, but not one to argue with the fact that the audio was actually working, I got my phone back last week.
And so it was actually working again..
Yep, the same problem again. What I suspect probably happened is that because of the various trips the phone has made, both in our internal mail, and also interstate once (possibly twice), it unstuck the headphone socket. But now there's no audio again, so I'm pretty sure the cause is infact a physical problem, that the audio socket is stuck in the 'plug is still in, so don't allow sound through the external speaker' mode.
Looking ahead, wouldn't one of these be a nice replacement.
One interesting side-note. While my rw6828 was away on its little holiday, I was given a plain old Nokia phone (a 3530?). Nothing remarkable, except that the battery would last for days. We live in a pretty poor reception area, which seems to suck other phone batteries dry in a day, so I was surprised that the Nokia would go for 3-4 days without requiring a recharge.