What the hell, anything to count time, right?! haha
Seriously, I remember when the whole idea came out in the Kingdom Ministry. Everyone talked about what a 'greeeaaaaaat' idea it was. I'm in somewhat tight with the local JW congregation, and I don't know ONE JW who opts to do this.
I mean, if you wanna waste time, why not stand on a street corner and be politely ignored? Why actively piss people off and trouble them with uninvited telephone calls?
I personally know JWs who have sworn off this lame tactic, because they feel that it automatically alienates a householder and makes them automatically unreceptive to the 'Kingdom Message' (they're right). Maybe this telephone witnessing takes off in some areas more than others. It would be interesting to study the differences in such areas to try to determine what make it fly or fail in the local JW community.