A kit for converting an existing pay telephone to additionally provide computer network access includes an upper housing unit that latches to a lower housing of the existing telephone, and a network adapter unit which includes a network computer and a control module that selectively disables a hook switch connection to a payphone electronics module of the existing payphone. A coin scanner and an escrow unit of the existing payphone are connected through the control module to the payphone electronics unit. The network computer, in combination with the control module, provides a stand by mode, a pay phone mode, a data mode utilizing an optional data port socket for connection of an external data device, and a network mode. The kit provides for remote management of network functions as well as payphone functions over a single telephone line. Also disclosed is a complete network access pay telephone.