Well the basic question has been answered with a yes.
However, as this is an iPhone, I would suggest calling customer service and make sure that there is no international bar that needs removing and that the correct bolt on and apns are in place before travel. It's much easier to sort out before travel.
Or get yourself a 3 PAYGo SIM and get your UK allowance used in USA up to 9GB of usage Enjoy!
I wish all OpCos were created equal..
Track usage, upgrade and get support with the My O2 appDownload My O2