According to a recent report from DigiTimes, Apple has ordered 15 million iPhone 5 to a Taiwanese manufacturer named Pegatron. This is not the first time that Pegatron is manufacturing iPhones for Apple. It is the same company that manufactured CDMA version of iPhone 4. Pegatron is expected to fulfil this order till September which somehow coincides with the previous rumors about the iPhone 5 launch.
This rumor came up from upstream component makers. Their sources also confirmed Apple is already started supplying components to Pegatron and Pegatron has started hiring manpower for manufacturing iPhone 5.
Apple did not released iPhone at WWDC this year which it normally does. And with so many rumors about September launch of the device, it seems that these rumors holds some truth. Time will tell the rest.