Preview at WWDC likely in June, followed by September launch.
Video Comparison of 'iPhone 5' Nano-SIM Tray and Buttons to iPhone 4S Parts
"iPhone 5" nano-SIM tray on top of iPhone 4S micro-SIM tray (Source: Nowhereelse.fr)
The comparison of SIM trays demonstrates how the micro-SIM used in the iPhone 4S/4 does not fit in the smaller tray that is reportedly being used in the next-generation iPhone. Like the nano-SIM tray, other parts shown in the video including the sleep/wake button, volume buttons, and mute switch are notably of a "gunmetal grey" color distinct from the silver color seen on the iPhone 4S. The video also shows the home button that was the first next-generation iPhone part to leak back in late April.
Apple is expected to introduce the next-generation iPhone with a media event on September 12, with the major new features of the device being a taller 4-inch display and a redesign resulting in a taller but thinner form factor.
Update: The video has been removed.
Update 2: The video is now available once again.