You'd have to start by looking at the charts used in the application you intend on using.
As far as I know the Australian apps are *NOT TO BE USED FOR AIR NAVIGATION* because of the charts they use.
The only digital maps I'm now aware of that *might* be covered are Jeppesen?
Jeppesen were recently fishing around looking for iPad Kneeboards and a deal on iPads so they probably have something for our region [or in the works].
Now that aside, if you want to just have the device certified for use airborne during critical phases of flight I'll defer to someone else