Unfortunately probably not since unlike churn there is no revenue reduction by deciding not to pay. There is only a positive revenue from those who do pay.
I don't follow your logic. The carriers are offering the watch plans since it's another profit center. I can't imagine the cost incurred by the carriers is much since it probably only involves linking some numbers on the back end. If they lose watch plan customers, they lose some profit. The more customers they lose, the less profit. So they might be better served by reducing the cost of the plan and gaining many more customers as a result.