I don't think there is any doubt that cell phone use while driving is a safety hazard, especially for texting.
However, I think the case can be made that GPS actually results in less distraction for drivers in unfamiliar places, as long as they are not adjusting the device while driving. Being told where to turn is much better than trying to locate a destination from numbers on buildings and likely ending up in the wrong lane. Taking over the task of navigation, the device allows the driver to concentrate more on the traffic situation.