I ordered the AT&T one x car dock from AT&T, thinking it would include the bluetooth audio dongle that was discussed in the various MWC videos. After more research and some unboxing videos I found, it apparently does not include it, and it's a separate accessory that is not available yet. I'm going to return it to my local AT&T store once I get it, but I'll test it first to see if it fits the E4GLTE.
From what I can tell, the car dock that's currently available for the one X does not have or use the pins on the one X. Instead there's an integrated wire clipped to the dock for the usb port. In one of the MWC videos, the HTC rep does mention that the pin dock will be coming later and a regular dock will be available at launch.