International version unlocked
main point of having an unlocked bootloader is that you will easily root your phone and the custom roms will run on your phone. HTC understands this and most of its recent phones including the HTC One X and One S have an unlocked bootloader.
The Tegra 3 versions are unlocked and we have seen many people quite happy with their custom kernels and custom roms. HTC went a step forward releasing the 35 variations of the phone customized for different telecoms around Europe and Asia and you can get these binaries here
It is clearly up to AT&T to offer to unlock bootloader but so far they weren’t that happy to meet the customers demand. Maybe it will happen but so far there are no indications of it.
It will be up to hackers to unlock AT&T One X bootloader but we are sure that sooner or later someone will manage to do that. In the meantime if you want an official unlock, you will have to get the non-LTE, international version of the One X.