As 3.0 GM has been released, all Australian carriers require specific settings for Multimedia Messaging (MMS). Below are the current MMS settings for Telstra, Optus, Vodafone, Three and Virgin. If these do not work for you, or you use alternative settings, please let us know!
You need to RESTART your iPhone for these settings to have effect.
Settings > General > Network > Cellular Data Network

[ TELSTRA ]
- APN > telstra.mms
- Username > [Leave Blank]
- Password > [Leave Blank]
- MMSC > mmsc.telstra.com:8002
- MMS Proxy > 10.1.1.181:80
- MMS Max Message Size > [Leave Blank]
- MMS UA Prof URL > [Leave Blank]

[ OPTUS ]
- APN > mms
- Username > [Leave Blank]
- Password > [Leave Blank]
- MMSC > mmsc.optus.com.au:8002
- MMS Proxy > 61.88.190.10:8070
- MMS Max Message Size > [Leave Blank]
- MMS UA Prof URL > [Leave Blank]

[ VODAFONE ]
- APN > live.vodafone.com
- Username > [Leave Blank]
- Password > [Leave Blank]
- MMSC > pxt.vodafone.net.au/pxtsend
- MMS Proxy > 10.202.2.60:8080
- MMS Max Message Size > [Leave Blank]
- MMS UA Prof URL > [Leave Blank]

[ THREE ]
- APN > 3services
- Username > [Leave Blank]
- Password > [Leave Blank]
- MMSC > http://mmsc.three.net.au:10021/mmsc
- MMS Proxy > 10.176.57.25:8799
- MMS Max Message Size > [Leave Blank]
- MMS UA Prof URL > [Leave Blank]

[ VIRGIN ]
- APN > VirginMMS
- Username > [Leave Blank]
- Password > [Leave Blank]
- MMSC > mms.virginvibe.com.au:8002
- MMS Proxy > 202.139.83.152:8070
- MMS Max Message Size > [Leave Blank]
- MMS UA Prof URL > [Leave Blank]