I'm no expert but, according to Wikipedia, Giffgaff has been an official carrier of Apple devices in its stores since 2014, so should work on iPhones. Also, if the iPhone is fully paid for, no reason why the Giffgaff SIM card could not be used. The iPhone mini uses the mini SIM. As long as giffgaff have a mini SIM (they all do nowadays), there is no reason it wouldn't work. I'm assuming your iPhone was purchased SIM free with no contract? It’s an unlocked phone so should work with any provider. It should do as long as its unlocked, which all new phones should be. Yes it do yes perfectly Yes. If you want to keep your old number you will need to port it over####[]