I also am encountering such problems on my One X when it loses signal in certain parts of my country (Singapore), but I suspect it to be because of my carrier and not the phone. My HTC one X has only lost signal twice after I got it back from HTC's customer care center.
I've had my OneX and AT&T for about four days. About 30 minutes ago I had a big fat X on ny signal indicator. I restarted the phone and its okay so far.
See, I have just driven using my old bb while phone is in repair (still - dont ask), the phone didnt drop signal once yet, if i did the same trip and called using HOX, it would drop the call a handful of times......really very annoying.