Preview at WWDC likely in June, followed by September launch.
New iPhone Rumors Reiterate Claims of Smaller Dock Connector, No Change to Screen Aspect Ratio
Despite some rumors to the contrary, according to our sources Apple still hasn't finalized the design of the next generation iPhone 5 (or whatever Apple ends up calling iPhone 5,1). No giant screen. No 16:9 aspect ratio. No metal back.iLounge previously claimed that the next iPhone would have a smaller, redesigned dock connector as well as a 4" screen that is larger in height only -- this would result in an adjustment to the screen's aspect ratio. The iPhone 4's design has served Apple very well, with the company selling millions upon millions of units. It is possible that the company will choose to stick with the successful design, albeit with some minor changes, rather than a wholesale redesign.
Once again we're hearing that if the screen size does change, it won't be by a lot (no larger than 4-inches). We've heard nothing to indicate a planned change in the aspect ratio either way (and such a change still doesn't make much sense to us).
Other recent iPhone rumors include a claims that the next iPhone will launch in September; another that it would use the same micro-SIM as current iPhones, rather than a new nano-SIM concept; and that the next iPhone will retain its physical home button -- a claim that iMore reiterates.