The latest version of the iOS 9 beta has brought some goodies, among them the new Wi-Fi Assist feature, which will recognise bad Wi-Fi connections, and use cellular data instead.
You can switch it on and off with a toggle in Settings, so if you've got spotty home Wi-Fi -- or jealously guard your data like your do your first-born -- you can disable it. Otherwise, it will just detect when you're using a network with limited or no connectivity, and use your mobile data instead. Before it switches, the Wi-Fi signal gets greyed out, giving you (some) notice that you're about to start using data.
Other new features include a new range of wallpapers, and the option to use Wi-Fi calling -- although no Aussie networks support that.