VTech CS5121 Cordless Phone System with Digital Answering Device and Caller ID The Vtech CS5121 operates on 5.8 GHz Digital spread spectrum technology providing unparalleled security, clarity, and range in cordless phones. This phone has a digital answering system that features remote message retrieval with up to 12 minutes of recording time. Also features caller ID and call waiting, storing up to 45 calls.