Cell phones are allowed to be used as you taxi to the gate but not when taxiing to the runway?

I think it has more to do with the fact that when you are taking off it is not always clear how long you are going to be on the ground. In the best case senario there is no line and it takes no more than a few minutes until you are in the air. The problem here is when do you tell people they have to turn off their phones? Is it when you are holding short of the runway? When you are three planes back. I am sure you have seen how long its takes people to turn them off when they are at the gate, imagine a plane ready to take off though one person is still yapping away about the last night to a friend back home. Would they have to abort the takeoff?

With that said, I have been on flights were the line was so long to take off the pilot has come on and said if you cell phone is within reach you can now use though you have to promise to quickly turn it off when I tell you. This was at JFK at 5pm where you can basically bet you are going to wait at least 45 mins in line.

oh ok that makes sense.