Apple will introduce new versions of iOS and OS X at its annual developer's conference.
Accessory Manufacturers Ramp Up 4th Generation iPhone Cases
Third party case manufacturers have already started creating case designs for the unreleased 4th generation iPhone. The so-called iPhone HD was originally leaked by Gizmodo in April with another major leak this month.
HardMac published this image from one of their contacts in China. The cases share the same rounded corner design of the leaked iPhone as well as additional spacing for a camera flash. A quick search shows some other early cases for the iPhone HD.
While these cases don't provide any additional confirmation beyond the original leaks, it does show that some companies are confident enough about the 4th generation iPhone design to begin producing cases for the product.