Abstract: A plastic number plate cover that can be installed from the exterior of the housing faceplate of a public telephone and which is resistant to tampering. The cover includes an envelope-shaped pocket into which a number plate or card is inserted, and opposed cantilever arms each terminating in a tab having a beveled edge. The cover is inserted into a rectangular-shaped recess on the faceplate when the tabs are brought into contact with a recess edge, causing the arms to flex and allowing the beveled edges to slide past the recess edge. The cover may be fixed or removable once installed within the faceplate, depending on the structure of the tabs.