Originally posted by RichLond:
You should be able to ticket BA using a QF flight number thus avoiding a service charge if you have already been ticketed.
It could be easier that this. As long as you don't require a ticket change, there is no change fee (aside from your first-one "free") charged. A change from "QF" to "BA" SYD-SIN-LHR should not incur this cost, but a change to "CX" SYD-HKG-LHR would.