Just to add SawMan, PLB's in Aus dont need to be registered. Marine EPIRB's do, as do ELT's. Marine EPIRBS HAVE to have the registration sticker attached here in Queensland, without it you get a pretty steep fine if you get caught.
Of course when you purchase a PLB here (I have one for trailbike riding) they actively encourage you to register it (mine is)
I think I also read in the AIP that coverage is worldwide for the 406mhz beacons, but may take upto 2 hours for a satellite to pass over in some places. I will have to check up on that one. May only be for the GPS enabled ones.