This, exactly. I live in Alberta, and the enforcement of this law is almost non-existent. I've never met anyone who's been pulled over for using a cellphone, nor have I ever met anyone who's met someone who . . . and so on.
I don't drive, but I am a passenger quite a bit (I carpool with a 1-hour-each-way commute), so I have plenty of time to watch other drivers. About 5-15% of them are interacting with something slightly out of sight. Strange how this is a superset of the drivers that drift slightly off to the sides of their lane every once in a while.
N.B: I don't doubt there are people that can multi-task in this fashion, i.e. use a cellphone and drive safely at the same time. I just don't believe that most of the people who do, can.