Greg F., think again. Under the US Constitution, states rights still exist. Whatever is not covered by the Constitution devolves to the several states. So, though I do agree with your intent, your argument is fallacious and inflammatory.

Given the federal highway system, it would seem to me the DOT has the perfect right to make such regulations. Virtually all DOT regulations have the safety of motorists and their passengers in mind and using a cell phone while operating a vehicle should fall under their purview.

Over the last twenty or so years the "several" states have been striping many roads other than federal highways. By striping, I mean mostly putting a double yellow down the middle as well as shoulder limiters. Why? Because if the states do not follow the "requests" of the DOT, ie, the federal government, the fed will withhold the funds for the upkeep of roads from the state that does not comply. The same could be done for a federal ban on cell phone use while driving. I'm all for it. Sometimes a little coercive pressure is just the thing.