With every new version of the iPhone that has come to market one thing we have seen repeatedly is the rumor mill churn and then the old gear gets phased out. Generally, when the iPhone and any other Apple product is close to replacement the delivery estimates for the old version start to get longer and longer. This has happened this week with the iPhone 4.
Early in the week the iPhone 4 was listed a shipping in 24 hours. Then that shipping delay grew to 1-3 business days. As of today there are no more shipping estimates offered, the iPhone 4 supply says in stock. That would seem to indicate that the iPhone 5 is coming soon and that stocks are dwindling on the iPhone 4.
Rumors peg the iPhone 5 for an October launch so that would put us roughly a month out. Rumors have also claimed that the iPhone 5 would come later in September. I would bet Apple starts dropping invites to reporters a few weeks ahead of the even to unveil the iPhone 5 so keep your eyes peeled.