Notice sent to O2 retail stores, via MacRumors:
The following is to advise that we are removing the old iPhone unitary between the 22nd August and the 12th September. This is a 3 week programme which will see all iPhone unitary swapped out for new iPhone unitary, and will of course prepare us for the launch of the new smart phone. At the same time we are installing an International Favourites bay to stores that can accommodate the unit, as well as replacing the existing magazine stand with a new freestanding stand.
September 13. That seems to be the day a new iPhone will be announced.