One of the indicators we always look for when a new version of one product or another from Apple is rumored to be on the way is the ship time of the model the new product will be replacing. When a product that has been around for a while and is generally available in plenty of volume to meet the demands for the consumer starts to see ship dates grow, it's often a good indication that the new version is near. Lately the ship times for the iPhone 4 according to the Apple site have started to lengthen.
The delivery time for the iPhone 4 earlier in the week was 1-3 business days. That hinted that the inventory might be diminishing thanks to preparations to move to the iPhone 5. Before that, 1-3 day estimate showed up on the Apple site the estimate was within 24 hours. Rumors still peg the iPhone 5 to launch in October with the chance of a cheaper version of the iPhone 4 in tow. Apple is doing very well with the cheap iPhone 3GS right now and will definitely want to keep something in that price range.
Foxconn is said to be getting 150,000 iPhone 5 smartphones ready to ship each day. Hopeful once the next iPhone lands there will be enough available to limit shortages. With other rumors claiming that all the US carriers will get the iPhone that may be wishful thinking. It was hard for AT&T and Verizon to keep the iPhone 4 in stock early on.