我工作 for a telecommunication company that manufactured PBX system for large scale companies many years ago . That audio telcom board, looks to me like it sends audio between telephone handsets used for VOX purposes 通过扬声器内部 units. It's usually between multiple "telecom lines" connected to telephone handsets like in a conference configuration. Those PC boards are real old school telephone 模拟 PBX systems 那 are not used anymore due to VOIP technology