Intercom on network to allow communication between 4 people

Probably a bit hardware related but worth a shout. A medical centre wants to set up an intercom type system. 3 rooms for Doctor, Dentist & Chiropractor all share 1 nurse/receptionist. They want the ability to talk to the nurse from the treatment room but not broadcast it to each of the other rooms. Ideally would like the nurse to be able to talk back also. Phones are an option. I was thinking of an intercom like Hosmart 1500FT LONG RANGE 7-Channel Digital FM Wireless Intercom System for Home and Office (4 Stations) but this does not have the ability for the nurse to be able to reply without changing channel and it will broadcast to everyone if not careful. Has anyone any ideas of a system that would do what I want? Have wife in the building and 3 spare ethernet cables in each room. The main cabinet is in the reception beside the nurse. Thanks