AT&T 5800 Accessory Cordless Handset, Black/Silver | Requires an AT&T 5830 or 5840 Expandable Phone System to Operate Expansion handset for use with AT&T model 5830 or 5840 5.8 GHz digital spread spectrum frequency-hopping technology Speakerphone for hands-free conversations 50 name-and-number caller ID history Sound Select for custom sound