Let's do some math - total cost of ownership in two years
Straight talk: $650 + 24 x $45 = $1,730
AT&T: $199 + $36(activation)2 + 24 x ($40 voice + $20 text + $30 data) x 10% (TAX) = $2,611
So yes, you save $881 for a better plan
If you put it like that then why the fUUk would you NOT buy out of contract? I bought a used 64GB 4S so I would have the flexibility to switch prepaid carriers as I move back and forth from the US, Panama, and various other countries. If I was obsessed with the 5 I would definitely buy a 64GB slab out of contract.