Updating that last post.... chewed through my prepaid T Mobile credit AWFULLY fast so I checked on the net and it seems I was given wrong information by the sales person. Calls to Oz are running at over US$1.50 per minute, not US$0.34!!
So back to calling cards and Skype, although T Mobile prepaid is the easiest for calls within the US which are fairly cheap, just not to O/S.