The only reason why I would buy an iPhone (or any smarthphone for that matter) is if the store offers some sort of discount for paying with crypto, something that encourages me to spend Bitcoin, otherwise, I wouldn't recommend doing it, it's way better and faster to just use fiat.

In the long-term, yes, it is possible, if Bitcoin goes full mainstream, and there's a demand for stores to accept Bitcoin as payment, you can bet that the big companies like Apple would not hesitate in adopting BTC as an alternative payment method.