Really, it comes down to what the definition of a phone is, and that will likely be written in the law. If someone wants to link to the actual text, our speculation might mean something, otherwise this is really just ranting.

IANAL (and certainly not an Australlian one!), but I also think there might be a case made for turning off the cell radio and then arguing in court that it was not a phone - that functionality was specifically disabled during the time in question. If you have a friendly magistrate, you hopefully get off scott free. If not, you can keep arguing your case and maybe you make some good law!