As @zitt said, if you have two wires (they don't even have to be twisted; the very old ones weren't) from the BT to the phone, the phone will work. That opens up a lot of possibilities for where to hide the XLink. (You want it to be close by to where you leave/charge your phones, so the bluetooth works well.)
Small sheetrock repairs are quite easy. I wouldn't hesitate to drill into the wall as needed to locate the XLink in a cabinet, over the microwave, or what have you. (We use an Xlink at home; it's nice. I didn't know until just now that it supports rotary dialing.)