At 60 miles per hour, your car is going 88 feet per second. In the time it takes for you to read a text message, say, 5 seconds, you have traveled 440 feet when you look up and see you need to stop. That's over 100 yards. And then you put on the brakes. At 60 mph, "a driver could stop the described vehicle in a total of 6.87 seconds (including a 1 second delay for driver reaction) and your total stopping distance would be 302.28 feet, slightly more than a football field in length!"
In total, two football fields. And that's if you are just reading. If you are writing, the result is worse.
Please don't. You are going to feel very stupid if you say, "I killed that person in order to read (or write) a text message."
Watch the video.