Originally Posted by gsheath
...Similar localised legislation and regulation exists in Australia aswell, as I'm sure it does in other 'member states' of the ITU...
You're correct about ITU...but if someones life is in emanate danger I don't think it matters if you use Mayday, PanPan, SOS, Help, or Ohmygod as long as you're able to get assistance.
Here is the US Coast Guards DSC Operational Procedures for Ships
You'll notice it says
A distress alert should be transmitted if, in the opinion of the Master, the ship or a person is in distress and requires immediate assistance.
On a side note here is an interesting story about Kayakers issuing a PanPan urgency call.