Pretty simple, like the page if you haven't already and fill in your details.
Your voucher code for the 30 day trial will be sent to the email address you have provided.
http://au.playstation.com/legal/detail/item540115/PLAYSTATIO…
Most important T&C's
Note: A credit/debit card is required to redeem this voucher. You will not be charged during the trial period. At the end of the trial your subscription will automatically renew into a 90 day membership where you will be charged. You may cancel your 30 day trial at any time.
At the end of your 30 day trial, if you do not take any action, your subscription will automatically renew to a 90 day paid membership in accordance with the Sony Computer Entertainment Europe Ltd Terms of Service and User Agreement and you will be charged €14.99 from funds in your SEN wallet. If your SEN wallet does not have sufficient funds the remaining balance will be automatically transferred from your connected credit card to your SEN wallet which will be charged for the remaining balance. Please visit the FAQ Page at http://uk.playstation.com/psn/support to learn more about how to cancel your subscription. You may cancel your 30 day trial at any time.
Thanks ABC for the information
http://au.playstation.com/legal/detail/item540115/PLAYSTATIO…
Most important T&C's
Note: A credit/debit card is required to redeem this voucher. You will not be charged during the trial period. At the end of the trial your subscription will automatically renew into a 90 day membership where you will be charged. You may cancel your 30 day trial at any time.