When is it illegal to use a cell phone while driving?

Using a cell phone while driving becomes illegal specifically when a driver is under the influence of alcohol or drugs. This is primarily due to the impaired judgment and reduced motor skills associated with intoxication, which significantly increases the risk of accidents. In this context, operating a vehicle while distracted—whether through cell phone use or impairment—can lead to dangerous situations on the road.

Other contexts, such as driving in heavy traffic or the use of hands-free devices, may not explicitly prohibit cell phone use, as long as the driver remains in control of the vehicle and is not distracted by the device. Additionally, "on public roads without a permit" is not a standard legal restriction related to cell phone use, but rather pertains to vehicle operation permissions. Therefore, the legal framework emphasizes the dangers of impaired driving alongside the distractions of cell phone use, marking it as an illegal action in these circumstances.