Motorola MD7001 2 Line 5.8GHz Digital Expandable Cordless Handset & Charger Accessory for MD7000 series 5.8 GHz frequency with digital signal transmission Caller ID/call waiting with 50-station memory; 10-station speed dial Functions as room monitor or intercom; conference call compatible Supports two-line operation when used with a two-line base system Additional handset compatible with Motorola SD4500 series phones