The optimistic take is that slow initial sales of the iPhone 8 line are a good sign for Apple, because it may mean more people will instead buy the more-expensive iPhone X.
Hope and Fear.
If the iPhone 8 had been a hit out of the gate, then I would have expected AT&T's upgrade number might at least have fallen less dramatically.
The company sells the vast majority of new iPhones to people who already own one.
If Apple and Samsung aren't persuading people to ditch their old phones right now, then their sales might not go up as quickly as investors expect.