Even though almost all phone jacks go on the walls, the term wall jack is reserved for jacks that are
designed to support a wall phone. Wall jacks have either plastic or stainless steel cover plates. The mushroom-like pieces at the top and bottom of a wall jack that fit into holes on the back of a wall phone and support the phone are mounting studs.
The original modular wall phones (middle row, right) had metal backs with slots and modular plugs in them that slid up
and down and mated with wall jacks.
Many recent models (bottom row, right — particularly phones that can be used on a table or on a wall — have a jack in their back inside a recessed space, and connect to the wall jack with a short cord that has plugs on both ends.
Some wall phones have short cords that are permanently attached inside the body of the phone.