Reuters believes that Apple has moved the headphone jack to the bottom of the new iPhone, to where it is also located on the iPod touch, and as such a smaller dock connector is required.
Two sources "familiar with the matter" confirmed that the 19-pin port is being used "to make room for the earphone moving to the bottom."
This would mean that the huge range of 30-pin accessories - such as speaker docks, chargers and game controllers - would no longer work with the new phone without some form of adapter.