pointless & unfair law suite against Apple;
The iPhone option "wifi assist" causes your phone to un knowingly use cell data instead of wifi. Default setting =? ON.
http://www.cnet.com/au/news/apple-faces-5-million-lawsuit-over-data-bills-caused-by-wi-fi-assist/


you can disable it by:
Settings->Cellular, go to the very bottom of the screen, assert "Wifi Assist" = off