The Korean automaker explains the idea in explicit detail in a recently published patent. The tech specifically "limits or disables the use of some of mobile device features which could cause distraction to the user," according to the abstract. Depending on variables like the vehicle's speed, the system determines what smartphone functions are safe to use, including texting or voice calls. Based on a plethora of permutations in the document, these restrictions could only be for the area around the driver's seat or for the whole vehicle.
The key to the patent is placing antennas around the vehicle and monitoring for cellular signals. When the system detects them, it can begin selectively deciding what features to allow on the device. The tech isn't a simple on/off switch either, and can possibly detect the time of day or importance of the caller to let messages though. The major downside to all of this is the phone would need to run a specific program or firmware for all of this to work.
With such a recently published patent, it might be years before the tech arrives in Hyundai vehicles, if at all. Still, this is an interesting solution. Of course, it would be far simpler if people just put down their phones. You can read the full description of the automaker's concept, here.