a) as few as possible. After all, they are doing you a huge favour.
b) your fair share, even though you aren’t paying for anything, which is the number of minutes divided by the number of people using the plan
c) As many minutes as you feel like using even if it ends up being somewhere between 1/2 and 2/3 of the plan minutes. After all, it doesn’t seem like the people with the plan are using them.
I figure the answer is somewhere between a and b. Even if the people paying for the plan aren’t using the minutes for that month…. does it give you the right to use them up? What if they have a flurry of calling in the last few days of the billing month? Can we say overage charges?