A report from the China Times says that the next iPhone – that would be the iPhone 5 – is slated for release in Q3, which lines up will with the traditional summer Apple launches.
The news part of the story is that the iPhone 5 has entered the "trial production stage," which means that the design must be largely finalized.
The China Times says that the design includes a metal casing – a switch back to the original iPhone's design over the iPhone 4's glass backing – that will improve antenna sensitivity.
Given the iPhone 4's antenna design troubles, turning even more of the casing into part of the antenna seems like a bold move.
Also cited as a design change is the 4-inch screen as an upgrade to previous model's 3.5-inch.