Up to 36 handsets can be used with up to 4 base units. Handsets can communicate with each other privately, independent of base and phone line. When used as two-way radios, operation is "full-duplex" like a phone -- no need to push a button to talk. Phone calls can be transferred from one handset to another. Includes 1 base, 1 cordless handset, and 1 cordless handset charger.