I made some "x-ray" images from photos in the fcc documents to get a feel about how the n810 is constructed. Notice the large empty area on the right side of the picture above the battery. This is behind the plastic antenna cover. The wifi/bluetooth antenna is visible on the left side in the second picture. Also note the pads on the far right side, so theoretically they could just solder a wimax module in. I think that they would make a new board design for the wimax model. They probably could have included the FM radio or a full size sd card if they weren't saving space here.