Preview at WWDC likely in June, followed by September launch.
New iPhone 5 Pre-orders Through Verizon Slip to September 26 Delivery [Update: AT&T at 14-21 Days]
That appears to be changing now, as Verizon is the first of the three major U.S. carriers to see its shipping estimates slip with new pre-orders now estimated to arrive on September 26.
AT&T and Sprint are still citing September 21 availability, but it appears that customers may want to move quickly if they wish to obtain the iPhone 5 on launch day without waiting in line at retail stores.
Update 9:15 AM: While AT&T's site continues to cite delivery on September 21 for new pre-orders, a number of customers are reporting that their confirmation emails are quoting shipment in 14-21 business days.
Update 9:55 AM: AT&T's site is now quoting the 14-21 business day shipping estimate previously reported by some customers.