Welp, I tried it one last time. This time the person I talked to told me again that it is device specific, and he supposedly had a list of devices he could pull up in his system, and the HTC One X was not on it. He could not explain why it works for some people and not others. He said the SGSIII was not on it either, but the SGSII was. I asked him if that list was available to customers, and he said no.
You have to have Wi-Fi turned off and connected only to your carrier's cellular network. The option to bill carrier should be in the drop-down menu right above the "Accept and Buy" button. I have an HTC One X on AT&T and this works for me with any app.
I just spoke to AT&T. The carrier billing option is available on smartphones right now. There is a push to enable it on tablets but as of today 1-15-15 it is not an option. AT&T either doesn't know if/when it will be available on tablets or doesn't want to say for sure.
Seems pretty backwards to me. I don't know about anyone else but I would rather play my games on my 12" tablet than my 6" phone.
Oh well, what can we do? HURRY UP AND WAIT/HOPE I guess.