In my physics lab, I used to do an experiment where you drop a ruler between someone's fingers and calculate their reaction time by the distance that the ruler falls.
This year, I added a new twist to that lab. I had all the kids go to their lockers and get their cell phones. They had no clue what was up. I had them text the alphabet with one hand. (Some whined about this, because they were used to 2 hands.) Their times for texting the alphabet ranged from 9 to 14 seconds.
I then did the experiment to measure reaction time (typical physics experiment.) But after that, I gave the kids up to 25 seconds to complete the alphabet. At some point during those 25 seconds, I would drop the ruler between their fingers. I corrected for any problems like "I dropped the ruler only when they were looking at the phone" - I dropped it at completely random times without watching the student.
NOT a single student was able to catch the ruler between their fingers under those circumstances. Not one. I had to switch to meter sticks.
So, to sum this experiment up: even when they KNEW I was going to drop the ruler (within 25 seconds, anyhow), and they were anticipating that the ruler was going to be dropped, they couldn't catch it while texting on a cell phone with the other hand.