Recently signed up for Telstra's XL Bundle, unfortunately, the code for 6 months of free Presto was nowhere to be seen.
After waiting weeks, I decided to take it up with Telstra's 24/7 Chat. The kind gentleman informed me that I could SMS the word 'PRESTO' to 0498 500 400 and receive the special code… PRESTO! It worked.
Also got a few friends to try this that aren't on the Telstra network, and all were successful.
Another code thanks to RogueWolf6 in case the SMS feature above doesn't give you one: TELB6MTH615
Just saw this promo on my T-BOX under information/news, don't think its targeted, find out soon I guess
Works perfectly thanks OP