Optus did that for my second phone. With the first phone, I had to request it. Optus then basically forwards the request to Apple and Apple unlocks the serial number of the phone in their database. To complete the process and unlock the hardware, you have to do a restore, as it's when the restore completes, that iTunes checks the properties of the serial number and accordingly unlocks your phone. So give Optus a call to do it, but give yourself time for it to happen and to do a restore.
As far as battery replacement, Apple does have a program in the US for US$79 where they will replace it. It's unclear if this program is global. Best thing to do is call Apple Care and check. I'll wager they can do it on the spot at a genius bar appointment at Chadstone.