According to at least one person who pre-ordered his HTC One X for AT&T from Best Buy, the retailer has now revealed the release date.
A gentleman named Miguel sent in the screenshots you see above to AndroidCentral last night showing that Best Buy wanted to let him know when his HTC One X was going to be released. While the company has been taking pre-orders on the phone, at no time was a release date for the device stated. According to the newest information sent out, the release date has now been set as May 6, but this is so far the only mention of that date.
Checks on the Best Buy site for the SKU number included in the email turn up no results, but as these pre-orders were only done in-store thus far, it could simply mean that it has not yet made it to the online store. We do suggest that you take this information with a healthy dose of salt until we hear something a bit more official from HTC or AT&T.