In a note to clients — as reported by “Fortune” (, Piper Jaffray analyst Gene Munster says the expected announcement of a new iPhone next month adds 6-10 million to Apple smartphone sales during the fourth quarter.

“We believe that a September launch could result in the final 10 days of the month generating 6-10 million iPhone 5 unit sales, which would likely shift out of December,” he writes. “We believe if the iPhone 5 launches in September, Apple could sell 26-28 million units in the quarter (this takes into account iPhone sales slowing dramatically from September 12-20, which is announcement to availability).

The Street is currently expecting Apple to sell 23 million iPhones in the fourth quarter, not 27.19 million.