New reports suggest that Apple will hold an event to unveil the next line of iPhones on September 9.
According to The Verge, September 9 has been a preferred day for Apple. In 2008, it unveiled a new lineup of iPods on that day; in 2009, it had its 'It's Only Rock and Roll' event. There's lots of history on the date for Apple.
Apple is expected to introduce two new phones, with bigger screens, new processors, maybe new materials, and even more.
However, there is no confirmation about the date and it likely won't be confirmed until just before it takes place.