Even though Apple has not officially mentioned any hardware update for the iPhone, evidence suggests that a new model (if not more than one) is indeed on the works. Exactly what new features it will bring is anyone's guess for now, but the latest crop of rumors claim Apple is planning to improve the device's 2-megapixel camera with its next-gen offering.
According to DigiTimes, a company called OmniVision has supposedly received orders for 3.2-megapixel CMOS image sensors for a new iPhone model as well as 5-megapixel sensors for "another Apple product expected to be launched later in the year." As with other anonymously-sourced rumors, you should of course take this with a grain of salt, though a separate report at Pocket-lint claims Apple is currently looking for someone to "drive the design, development and integration of camera modules across iPhone and iPod."
But merely pumping up megapixels won't make the iPhone camera much better, so hopefully they'll also pay attention things such as optics, image stabilization and improving low light performance.