Sometimes prepaid is a bit more expensive because you're paying for 28 days and not a month. You basically have 13 cycles per year instead of 12 (28*13 = 364 days)
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.
I don't have a cell phone subscription either. I use prepaid which actually is cheaper.