Apple is right on schedule to release the next generation iPhone in summer of 2010. Unreleased iPhone hardware version 3,1 has been logged by PinchMedia this month in San Francisco. This means the company is already field testing hardware for the next model iPhone.
In the past, Apple has field tested other iPhone models 6-8 months before release. The jump in hardware designation from 2,1 to 3,1 indicates the hardware update from the 3GS to the next model will be significant.