Carterfone

The Carterfone decision (1968) was a landmark ruling by the Federal Communications Commission that forced AT&T to permit customers to attach third-party devices to the telephone network, overturning AT&T's long-standing prohibition on non-Bell equipment. The case involved a device called the Carterfone, which connected mobile radio systems to the telephone network, and the ruling established the principle that the network operator could not control what equipment connected to its infrastructure.

The Carterfone principle — that infrastructure must be open to compatible attachments — is the ancestral form of network neutrality. It recognized that the owner of a coordination infrastructure cannot be permitted to use control over the physical layer to dictate what services, devices, or innovations are permitted at the edge. The erosion of this principle in broadband — where ISPs routinely block, throttle, and prioritize traffic — represents a reassertion of the very monopoly power that Carterfone was designed to prevent.