Roll the unused minutes on to the following month. Not necessarily a discount only more minutes.
Why not. After all customers are paying for an allotment of minutes based on their plan. Why shouldn't they roll over. Take your home budget for example. Just because you have planned your budget well and you have saved $100 at month-end you gey to carry IT over to the next month. Why should minutes expire?
I'd like to see this put on postpaid, but have a limit of how many minutes it saves on your plan. Say once it reaches 1500-2000 minutes you have it saved in your plan for emergency purposes. Prepaid has something similar to that in the case that when you add Boosters for calling they don't expire, so they can carry over indefinitely as long as you have the account active and top up your base plan. Either way it gets my vote :)