There were some discussions regarding HTC’s support (or lack of) for the One X on AT&T in terms of the company not unlocking the bootloader of the American version but now the device has been unofficially rooted by the community.
While you will still not get access to the bootloader, at least you will now be able to have root access on your phone for all those mods waiting to be applied. It’s still something to help you get through the waiting for custom ROMs and whatnot. If root is something you need to have on your AT&T (and not only) HTC One X and you understand the risks, head over to the source link to find instructions as well as the root download.
Source: XDA Developers