After iMore broke the story on Monday that their source said Apple will hold an event to launch the iPhone 5 on September 12, a number of other trusted websites also reported that their various inside sources confirmed the date (including The Verge, The Loop, Reuters, Bloomberg, the New York Times, and CNN). In addition, Sharp said today that its displays for the next iPhone are ready to go and that it will begin shipping them in August. Which also seems to be a confirmation that the new phone will be out in September.
iMore said that Apple would also announce an iPad mini at that event, and that the iPhone would be available for purchase on September 21. But they said there was no word on when the iPad mini will be available for purchase. Some speculated that the mini would also be available on September 21, but the International Business Times makes a convincing case why that's unlikely. Simply put, the iPhone 5 will itself cause long lines and an overwhelming amount of traffic to stores and to Apple's website. Adding an iPad mini to the mix would result in a terrible customer experience because the crush would be doubled. In addition, the companies rumored to be manufacturing the display have given their timetable for ramping up production, which indicates that the iPad mini would be available in late fall for the holiday season.
The IBT article also gives a comprehensive overview of everything that's known about these forthcoming devices, including a gallery of the images that have been leaked.