Maybe you are confusing Verizon here? until January 8 you can still sign a contract and get an iPhone for $200 with ATT; there is no loophole and no reason to buy outright. After January 8 you can no longer do this, however your monthly rate remains exactly the same. You can/could also choose to pay next, but you will have to pay the next installement plus an additional monthly fee (on top of your plan rates), which is what made Next more expensive, by far, than contracted plans. The shared plans "get around this" by adding a reduction to your monthly cost; this was ATT's way, when introducing sahred, to get people to choose tiered data because, when comparing costs on multiple lines, it becomes cheaper, particularly when multiple lines require more minutes.
EDIT: I keep saying iPhone and $200. What I am really meaning is "you can sign a contract and get up to $450 off a new phone".