A:Answer (From the manual): The telephone can support up to five DECT 6.0 cordless handsets (AT&T model DL70019, sold separately), cordless headsets and speakerphones (sold separately). Visit https://telephones.att.com/accessories for a list of compatible DECT 6.0 cordless headsets and speakerphones. Each new handset, headset or speakerphone must be registered to the telephone base before use. You must register each handset, headset or speakerphone separately.