We generally do not do short codes due to their expense and complexity of compliance. We can acquire short codes for you, 8 digit numbers start at $800- $1000 setup and $250 - $300 per month. 6 digit codes come with a hefty Australian tax component which usually puts them out of reach of all except large organisations and government.
For information on premium billing and short codes see this link
Min charge for a user to text to a short code is 55c which is not covered in their plan. Carrier takes all of this. There is no such thing as a 0 rate short code in Australia.
Compliance requires the display of the cost to text in and a live info line where the short code is advertised.