The code to get the Huge Materia in Rocket Town in Disc 2 is: Circle, Square, Cross, Cross. On the PC, it's OK, Switch, Cancel, Cancel (Enter, Delete, Insert, Insert with default controls).
I can now confirm the code on iOS (iPad, iPhone, iPod touch) and Android is: A, X, B, B. Note that this doesn't match with other versions, as Cross on the PlayStation version would correspond to A on the mobile version, meaning it would have ended in A, A; not B, B. They went and switched things up to trick people... :)