Regardless if you have an international HTC One X or its U.S. variant on AT&T, you might be among the unlucky few to have messaging notification problems. Seems like the bug doesn’t notify you at all of an incoming text and the only way to see if you have a new SMS is by going into the messaging application.
HTC is reportedly aware of the issue which is affecting a “very small number” of owners for both the international version and the AT&T variant. The Taiwanese phone maker already has an update in the works which is supposed to fix this issue but a timeframe for the roll-out process is still unknown. Until then, if you know you experience this issue, make sure to regularly check (yourself) for a text.