Dear Asbestos,
The case you have given shows that the 25$ plan is expensive for him. He would have been better off not taking the 25$ plan. In order to get the best out of plan he should use it in such a way that the discount of 40% is more than the flat payment of 25$. This discount is .64$ for calls less than 3 min and only .32$ for any extra min. Thus the max saving will happen if only calls less than 3 mins are made. If calls less than 3 min are made everytime,than the total expense would have been
=1.6*60=96
now suppose he pays 25$ and takes the discount
cost of calls made=1.6*60*.6=57.6
total money to be paid=57.6+25=82.6
saving made=96-82.6=13.4
I hope i am clear
This problem is a constant dilemma that a mobile user faces while taking a special plan