The closest option to this is the flex data plan, where you only pay for the tier you consume. We moved from a model where folks paid for the minutes they used to the current process of buying a bundle of minutes monthly, as people preferred the regularity of a fixed bill, and were happy to pay the 'insurance' premium not to have bill shock in some months. Same with Data; folks loved the cheap 5GB plans, not so much because they used 5GB / month, but because they were sure never to go over.
Buying a bucket of minutes is still possible on prepaid, but they are relatively expensive - best price is about $0.15 / minute if you have an add-on of some sort, else you pay $0.50. I expect data would be the same; if you expect to consume every byte of data you purchase those bytes will be more expensive than buying the insurance plan.
Like a ski pass or golf membership, the fact you did't get to ski or golf every day does not lead to you rolling over your unused days to next year.
NFtoBC
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