This recent change can cause those with iPhones with IOS 9 to potentially be hit by huge data overages even when using WiFi and I felt it important enough to make you aware of it.
I was wondering why my cellular data usage recently skyrocketed on my iPhone, and this explains it, as the default setting is to have this “Wi-Fi assist” enabled, causing data to be split between WiFi and Cellular data by default, and on the iPhone 6 this setting is under Settings/Cellular at the bottom of the screen. Newer Android phones have similar “Wi-Fi Assist” functionality, but on those devices is disabled by default, so be aware of the implications if you do decide to enable it.
http://www.businessinsider.com/apple-is-facing-a-lawsuit-over-its-wi-fi-assist-feature-2015-10
