[AT&T, Rogers HTC One X, Telstra One XL] hx4700 Killer:
I will start off by saying I had a picture. I know I took it with an old phone but when I started it up again a little bit ago it was not there. Don't know how I managed that. I have to open it again in a few days when my new power button shows up so I will take photos then and add them. For now you get the crappy paint diagram.

I Performed this on an AT&T HOX released back in May Model PJ83100.

This fix gained me FULL or near full WiFi signal in places I was getting ZERO signal before. I could not get WiFi at the back of my house on the inside, now I get connected in my back yard. I really thought this was going to be a waste of time but boy was I surprised at the signal strength after.

I TAKE NO RESPONSIBILITY IF YOU BREAK YOUR PHONE DOING THIS OR IF SOMETHING HAPPENS IN THE FUTURE. YOU ARE TAKING THE SAME RISK I AM IN TRYING THIS!

Basically I popped the phone open with a thin guitar pick run along both sides from bottom to top pretty much like every video shows. (DO NOT USE A HOOKED OBJECT, you will be sorry!!!)

On the inside of the back of the case on the left edge just below the usb port hole are two gold contacts. They are the pair closest to the edge of the left side. I saw the letters BT with some numbers before/after them printed on it.

Starting with the lower of the two contact points (farthest from USB hole):

I got out some tinfoil and used an exacto knife to cut a 2 - 3mm wide strip. At one end I made it the same width as the gold contact but twice as long and then folded it over on to itself over that wide section to make it twice as thick at the contact point and the same size as the contact. I took a 3 inch strip of some scotch tape and attached it to some clear plastic. In my case the address "window" on a piece of junk mail. I then used the exacto to cut the strip of tape in to thin strips about 6mm wide. I took the foil piece and laid the wide end over the contact point and let the thin 2-3mm "tail" run along the black cover over the real antenna towards the bottom of the phone. Basically from the contact point straight towards the bottom. I had to dry fit it and trim the thin part (the tail I mentioned earlier) to length so its just as long as the black material under it that covers the actual antenna. I then used a small strip of the tape I trimmed to completely cover thin part of the strip except for the wide part at on top at the contact point.

The Second contact Point (closest to the USB hole):

On this one I did something similar but instead of it being straight it was more ad upside-down "L" shape. The hook in the bottom of the L was the part I put over the contact point and again made it double thick and the same size as the contact point but a bit longer. I then cut the longer "leg" of the L at 2-3mm thickness same as the first piece of foil. There is a space between the BT/WiFi antenna's black insulating cover and a big black square covering nearer the middle of the phone that matches up with it being behind the battery and the NFC antenna just above that. It is the actual polycarbonate of the phone. In other words there are no antenna or anything else there its a white spot on my white phone. I laid the 2-3mm leg in that area directly against the back of the phone and used another thin strip of tape that I had cut similarly to above to cover it. This piece of tape I let run a little longer above and below but not over the part of foil on top of the contact point.

Finally I took a full width piece of tape and went across both foil legs up to the contact point of the first, smaller piece of foil. Again making sure to keep the contact point uncovered. Over the rest of the L shaped piece I used a smaller thin strip of tape above the wider piece to cover the rest of that one a second time.

Bottom line you DO NOT want either piece of foil touching the other and you DO NOT want any of the foil except the area on top of the contact points exposed where some part of the electronics of the phone could touch it and fry your phone.

I used scotch tape if you want to, use electrical tape. I wanted something that would come off easily leaving behind little to no residue or doing damage coming off.

If you have done this correctly you should have something that looks like this:

Adding:

I have seen others talk about using foil or solder to fix this. I am not reposting someone else's idea. I haven't seen anyone do anything with foil other than cover the contact point area to make it thicker and reach the gold prongs on the board.

I'm also adding that there was no real science or theory behind this other than the foil would increase the antenna surface area and the double thick part at the contact point would make a better connection with the phone electronics.