Apple has always made use of its Worldwide Developer Conference (WWDC) to unveil the iPhone. The iPhone 3G and the iPhone 4 were announced at WWDC, but this year they were pretty much focused on software and planned to launch the new iPhone 5 sometime in September.
The latest rumor states that the iPhone5 will be launched somewhere in September this year. The new iPhone is in final testing and is due in September.
There also a report from Reuters dated back in April, 2011:
Apple Inc suppliers will begin production of its next-generation iPhone in July this year, with the finished product likely to begin shipping in September, three people familiar with the matter said on Wednesday.