VTech CS6509-15 Accessory Cordless Handset, Blue | Requires a VTech CS6519, CS6528, or CS6529 Series Cordless Phone System to Operate Accessory handset only-requires a VTech CS6519, CS6528 or CS6529 series phone to operate Know who's calling with Caller ID/call waiting-stores 50 calls: Handset displays the name, number, time and date of incoming calls. With the touch of a button, the handset speakerphone makes hands-free conversations easy. Backlit keypad and display: The entire keypad illuminates along with the LCD screen, allowing for easier viewing in dim light. ECO mode power-conserving technology: Power-conserving technology manages consumption for optimal battery performance.