According to report from MacRumors, Apple may start pre-orders for the next iPhone on Friday, September 14. This conflicts with an earlier report from iMore which suggested the iPhone would be available to order shortly after the September 12 event. If we look at history for guidance, then Friday is the likely pre-order date. When Apple announced the iPhone 4S last year, it kicked off pre-orders on the Friday after the event.
We will be covering the event tomorrow and will have all the details as soon as Apple announces them. Regardless of the timing, the upcoming iPhone launch promises to be the biggest one thus far.