Yes, you're right--that's still too much time and attention directed away from the road. Highway speeds are about 25 m/s. In the 3-4 seconds it takes to send this reply, you could easily travel the length of a football field.

People (youth and otherwise) should realize that not responding immediately isn't the end of the world. The problem is with our culture these days, we all expect answers right away. Probably cell phones should have a "Busy" profile you could select from the menu (like the "Normal", "Loud", "Quiet", etc) that would send an autoresponse asking the caller or texter to try again later. Or simply wait until you're not driving to reply. Or turn it off. It's commonsense, but most of us don't use it anymore.

The comment remarking that a telephone call has a rather imperitive demand to be answered is true. Menotti wrote an opera about that. What might be a good remedy is that a phone be worked out to give a special shrill signal for emergency calls only and other calls could be answered when the situation was safe.