Adding to the speculation: T-Mobile has reportedly issued its own vacation blackout for Sept. 20-22. And, Japan's Nikkei reported earlier this week that the 5S and 5C will go on sale in Japan on Sept. 20.
The reports confirm the timeline postulated earlier this month. AllThingsD reported that the next iPhone would be unveiled at a launch event on Sept. 10.
On the iPhone trade-in front, Best Buy appears to have front-run Apple. During the Labor Day weekend, Best Buy will offer a 50% discount on iPhone 5 purchases with a 4/4S trade-in and 2-year agreement.