Well Apple has always used the WWDC in San Francisco to unveil new iPhone. The iPhone 3G, the 3GS and iPhone 4 were all announced during WWDC but this year Apple choose to focus on Software. According to latest rumours the next iPhone will be launched in September. It is not sure whether the new device will be a completely new handset the iPhone 5 or slightly enhanced version of iPhone 4 to be named as Apple iPhone 4S.
If the new iPhone is announced in September then its arrival will coincide with new version of iOS 5 operating system which ignites iPhone, iPad and iPad touch. The iOS being updated at WWDC eventually has provides time to developers to upgrade their apps before the new iPhone in September.