Apple knows that people now expect an iPhone refresh around September every year. This reflects in the invite sent this year. Notice how it says "It's almost here." with no reference to the iPhone unlike last year.
The date iMore learned about was right after all. And once again, Jim Darlymple was right with his confirmation.
The shadow of the 12 in the invitation graphic forms a "5", which is rather creative, but I'm disappointed that they might be calling it the iPhone 5 instead of dropping the numbers altogether or calling it the iPhone 6. After all, it's the 6th-gen iPhone while the 4S was the 5th, no matter how small the upgrade.
Anyways, the event will be held at Yerba Buena Center for the Arts in San Francisco at 10 am and I cannot wait. There are still buzzing rumors about a smaller iPad; however, it is said that there will be a separate event for that. So far we haven't seen any credible leaks of the device, although very reliable sources have reported that components are in production already.