It is, but the wiring is a bit odd.
The main BT wire runs into the garage loft (where a master socket is tapped into the line) and then it carries on to a very old BT junction box on the outside of the house but it's terminated there.
I'd like to get BT out to check but they always threaten charges etc.
It was like this when I moved in, I just replaced the faceplate with the latest version.