I suspect the OP means prepaying for the year. AT&T is like $25/mo for 5GB data + unlimited everything else if you pay upfront for the whole year ($300). Prepaid MVNO plans are even cheaper.

No that's not what I mean. And I'm not in the US. A €20 prepaid data bundle here on orange is much larger than a €20 contract. And the prepay has built in overcharge protection.