The only risk of using these codes is there risk the phone could become a brick/blocked if Telstra find out. The phones IMEI which Telstra has can be used to block phones from Australian networks.
We looked at using unauthorised codes for some locked 3G phones a few years ago and were warned of the risks by an ex-telco employee. Telstra is known for blocking phones/IMEIs it deems as suspicious or illegal activities. Some unlockers are also scams to gain credit card/personal information.
Instead of unlocking through Telstra, it was cheaper in the long run to buy a 4G phone outright and switching mobile provider.
