So about $600.99 then? What a bargain. The $449 price is cheaper than that. (Assuming you are on AT&Ts more recent plans where they charge you $25 more for having a subsidized, on-contract phone.)
For an iPhone 5S you pay $0 up-front and 24 monthly payments of $27.09. Of course, $27.09 * 24 = $650.16, the unsubsidized phone price.
You can, of course, still buy phones on two-year contracts instead of paying monthly. In that case you'd pay $199 for an iPhone 5S, in addition to a (lower) contract hit.
So for an iPhone 5S on a 2-year contract with a 10GB plan you pay $199 up front and then $25/mo for two years with a grand total of $799 over two years.
AT&T's new pricing structure is a mess