I just installed a 15 phone X16 system (+ cordless adapter) and needed to wall mount 5 of them. The spacing of the pins is not meant for a NA wall jack but is the same as a standard mud ring. However, the plastic is too thin on the mounting holes which creates a wobble. I used two of the studs furnished with the phones and Commscope (formerly AT&T, Avaya, Lucent, Systimax) M10L-262 wall plates which have a deep recess for a number card and screw. The metal collar on the stud fits perfectly in the screw recess and lets you set the stud to the perfect depth to hold the phone securely. I bought a pack of 10 wall plates for $12 on ebay (still listed). The jacks themselves can be found on ebay too or you can just crimp an RJ-11 on the cable. Using this wallplate makes for a professional installation and the phone is solid as a rock.

Why do I have to press one for English when they're just going to transfer me to someone I can't understand anyway?