Abstract: The present invention provides an extension device capable of working with a common digital telephone and providing functions of easy text input, data carrying, exchange, storage and editing. The telephone extension device includes a data exchange unit which communicates directly with a digital telephone; an electric note card (similar to a Personal Digital Assistant, PDA) which includes a display unit for showing information, and a standard computer keyboard for easy and fast character input when connecting via the data exchange unit to the digital telephone. Therefore, the extension device for digital telephone is easy for data input, easy to operate and carry, and useful for recording telephone information.