They say using cellphones (or smartphones for that matter) is bad for the human brain.
First, it burns it… secondly, using address books makes you forget the numbers, and researches found that remembering phone numbers can improve your brains performance.
Yesterday I had a call and it was a "sorry, wrong number" kind of calls… and I suddenly thought about it, that with today's address books, there are very few "wrong numbers".
Think about it. When was the last time you got a wrong number?