A unitary handheld portable module includes a keypad for entering data and a display for displaying data. A base module is configured to be coupled with and communicate through a telephone line and includes a keypad for dialing a telephone number and a display for displaying information. The portable and base modules are configured to have a mounted configuration in which the portable module is removably mounted on the base module and covers the base module's display, and the modules communicate with each other for the portable module's display to display information relating to operation of the base module.