AGree. in fact I now just leave my phone in Roaming mode all the time. I used to have it OFF when home in Aust and turn on before going. But it's easy to forget, and a couple of times, I've gone to do it at the airport and get the Optus widget sating "Service Currently Unavailable.. please try again later" The problem with later... is I will be on a plane and the next time my phone is out of flight mode... it's too late.* Switch your iPhone to international roaming before you leave Oz.
Also send them a copy of your Travel Insurance policy with contact details, as well as a copy of your SmartTraveller Trip registration.* Email a copy of your itinerary (dates, places, hotels etc) to your next of kin
Wandering slight off-topic... but still a key part of my Pre Travel Checklist... If the worst should happen while you're travelling, instructions where to find your Will. And just as important these days... a secure way to access all your online accounts, logins and passwords which will make things much much easier for whoever is looking after your estate.
I use LastPass which has a feature called Emergency Access. Essentially a dead-man-switch for my secure LastPass online vault where all my stuff is stored. I set it up a while ago and my Brother got an email with a one-time link and instructions should they ever be required. If I die then he then invokes the Emergency Access request. This sends me an email asking to CONFIRM or DENY access. If 72 hours pass with no reply from me, then he gets full access to my LastPass vault. You can configure the timing to be whatever you want.