Capacity: 4 Main Lines (Trunk Line/ P and T) and 16 Extension Internal/External Music on Holding, Operator/Auto-attendant Mode, Remote Programming Day/Night Mode(Manual), Music & Ringing Recordable OGM(outgoing message), Music Duration 20 Seconds Caller ID, Call Transfer, Call Forwarding Manually, Outgoing Call Transfer, Power Failure Transfer, Specific Main Line (C.O./Trunk Line) Dialing, Three Way Conference, Do Not Disturb, Auto/Manual Dial-Out Mode