You can register for a new Presto account on their website and then enter the promo code to get the first month free.
https://community.presto.com.au/t5/Getting-Started/Welcome-t…
I believe you are required to enter your credit card details during the verification process, but you can enter the promo code to get a $0 subscription for the first month. Afterwards, simply cancel the account before a whole month has passed (just go to your Account page and click on the "Close My Account") - https://community.presto.com.au/t5/My-Account/Suspending-or-…
I went with the same process above (they gave me 2 codes; I already used 1 to review the service and the other to give it away)
Just a note for the weary. This giveaway is only valid if you have a Presto account (are already a subscriber). Not really a "FREE" competition. It doesn't claim to be one don't get me wrong, but not much of a competition win really if you currently are not a Presto member. Also the subscription rates are $20 per month so the win is $20 credit really. Worth it if you're a paying member otherwise not much of a competition.