HTC One Developer Edition unlocks the SIM, bootloader and your wallet all for $649
Only buyers with a U.S. zip code can purchase the HTC One Developer Edition, which is being produced in limited quantity. Outside of the unlocked bootloader and SIM, this is the same phone that your buddy down the street will pay a lot less for, on contract. If you plan on building apps for the phone or you are going to be tinkering the heck out of it, you might find it useful. Otherwise, the regular carrier version should suit your needs.
source: HTC via Engadget