While unsubsidized mobile phones and smartphones are pretty common in other regions of the world, it still looks like U.S. Americans are pretty much sold to its carriers, instead of going carrier-free. As a matter of fact, and I know it from my own experiences, it's pretty hard in the U.S. to get a SIM card sans device. Nevertheless, as said it's common in other parts of the world to go contract free. For instance have we "O2 My Handy" (handy is the "German term for mobile phone) here in Germany which works independent from a mobile phone contract and which allows you to purchase a mobile phone which is financed by way of credit. This means you pay upfront a small amount and the rest 24 months equally.
Looks like HTC is also trying something similar in the U.S. now where it's offering - for a limited time - an unlocked HTC One; direct for US$ 0 down and 0 % interest on financing for 24 months. The total two-year price is US$ 600 which is handled in 24 US$ 25 installments. And if this is not enough, the unlocked HTC One is already running on Android 4.4 KitKat.
Definitely an interesting approach by HTC America to maybe gaining more independency from carriers and getting directly in touch with its carriers. However, it's a question of the customer's mindset is this approach will become a success; therefore it's just a trial which ends 29 December 2014.
Cheers ~ Arne