Japanese blog Macotakara [translated] is claiming that the iPhone 5 production has commenced in China and considering a lead time of about 2 months, September seems to be the probably launch month. The site had reported on a similar timelines for the new iPad back in January. The iPad 3 launch happened in March thus indicating a solid two months lead time. But, this might not be the case with iPhones as lead times may differ significantly.
Previously, the Wall Street Journal had reported that the production of iPhone 5 would start sometime in June and that all signs are reporting towards a late September or early October launch.
Some supposedly iPhone 5 components have been leaked which indicate that the next-gen iPhone will carry a two tone back panel with a central metal plate notes Mac Rumors.
More on iPhone 5 here.