AIPHONE NIM‑20B 20‑Call Audio Master Station. The NIM-20B supports up to 20 door stations, sub stations, and ceiling speakers. It provides Selective Call, Group Call, and All Call. The NIM-20B has a handset for privacy. The NIM Series is a Lamp Memory Intercom supporting a single master station and up to forty sub stations. Calls to the sub stations can be placed selectively or via All Call from the master station. Features 

• Mix and match up to 20 door stations, sub stations, and ceiling speakers to create the desired communication solution
• Call queuing
• Select different transmit and receive volume levels
• Selective, Group, and All Call PTT or handset communication