A document has leaked from Best Buy onto the internet which reveals that the iPhone 5 may launch on October 1st. The document indicates that the iPhone 5 will be available on the Sprint network on the 1st which it does not currently reside on. So on October 1st we know that the Sprint network is expecting the launch of the iPhone 5 so that would also confirm that the iPhone 5 will also launch on other networks that day or earlier. The document reads specifically:
Now the document does say that the dates are subject to change which would be expected as Apple has not yet announced the iPhone 5 officially.