1. To get a 4S, and to get it now, or do you mean
2. Is there an issue with an Australian sourced one?
1. is up to you, 2. I am unsure if there are any gotchas with an Oz one, given that with Siri, that may or may not appear on ours. If it doesn't, and you update iOS5 versions from here, will that be an issue from a NZ IP address on a non NZ iPhone? I do not know.