AT&T E580-1 Accessory Cordless Handset, Silver | Requires an AT&T E5000 Series Expandable Phone System to Operate 5.8 GHz frequency-hopping digital spread spectrum signal For use with AT&T E5860, E5865, E5900B, and E5965C phone systems Caller ID/call waiting, 50-number caller ID memory; image ID 50-number phone directory; intercom, conferencing, call transfer Personalized ringer options; handset message retrieval speakerphone