A telephone headset adapter includes a deck with a top surface for supporting a telephone. The deck is placed underneath a telephone, and the weight of the telephone is applied on the deck and stabilizes the deck. The deck includes a primary or fixed deck portion and a movable deck portion. The movable deck portion is coupled to the fixed deck portion by an extension slide. The movable deck portion is movable along the extension slide to vary the width of the deck. Thus, the deck can support and accommodate telephone sets of various sizes and configurations. Routing channels are also formed within the top surface of the deck for receiving cords that are used with the telephone set, handset, headset and accessories, thereby minimizing cord tangling and clutter. An electronic housing is removably coupled to an end of the deck. The electronic housing contains adapter components for coupling the telephone to the headset or handset. Alternatively, the adapter components are housed within an interior portion of the deck.