No, it's an unwritten rule. The written rule says, "No texting while driving."
The unwritten rule says, "We can't really monitor the inside of your car, so just don't drive badly and we won't pull you over for texting while driving."
Note that what that really means is: "We can't really monitor the inside of your car yet."
There have been idiot legislators that have suggested linking into the onboard computers in cars to see if people have been speeding. How long until one of them suggests that since web cams are so cheap and most cars have onboard computers, lets record people while they drive?
That’s not an unwritten rule. that’s just you whining for a week now defending an indefensibly stupid behavior that gets people killed. Get over yourself.