I assume the father has made a complaint to the police over the matter. The police need to investigate whether any charges could be laid, but then whether there would be good prospects of a conviction. If the matter gets to full police investigation stage, witness statements need to be taken, identities need to be confirmed, a full course of events needs to be determined and evidence gathered. The easiest way to assist a police investigation is for alleged offenders to make a full and frank admissions which then becomes police evidence.
Now, here is the interesting situation. The alleged offender resides in one state and the alleged offence occurred in another. While the alleged offender provided details to the boy's father and then rang to apologise, we are assuming that these details were given honestly and correctly. As a defence, the fact remains the alleged offender's identity must be proven first. Many court cases fail this way and this is one of the reasons why all drivers must carry their licence while driving to ensure that identity may be confirmed.
After all, in that situation it would be very easy to say on the night "sorry about that..." "what's your name?" "my name is Joe Blake, but I have a new phone and don't know the number yet" get his details, then, put your phone to private, ring the Dad up a few days later and apologise again using that false name.
Any court action must occur in Queensland (the SA Courts have no jurisdiction to preside over Queensland offences) and it is unlikely that the police would extradite someone over a matter like this. However, if it did go to court, then an "in absentia" verdict could be delivered if there was strong enough evidence, or an arrest warrant issued. Unless the crime is a very serious nature then the court system is clogged up and so if a charge was laid and the alleged offender not in court, it is likely the charge would float around in the ether until the alleged offender made a trip to Qld, got pulled over for a traffic infringement, the cops saw the outstanding matter and before you know it, the alleged offender is sharing a cell in Boggo Rd (is that jail still going?)
Now Queensland police may make a request to SAPOL to interview the alleged offender to obtain a statement and they are quite within their rights to do that.
There is a reason why lawyers tell their clients to remain silent.