Your theory should be testable by showing a dip (or some kind of deviation at least) in the sales of the GS3 just prior to the iPhone announcement. However I believe (and I'm sorry, I'm going purely from memory here) that sales were accelerating then too. Personally I think there was just a giant ad spend on all sides that caused a lot of consumers to decide to get a new phone. What phone they chose was down to what they liked when they walked in the store.