PABX/Intercom
A private automatic branch exchange (PABX) is an automatic telephone switching system within a private enterprise. Originally, such systems – called private branch exchanges (PBX) – required the use of a live operator.
The female hand presses a button doorbell with camera and intercom 
Interphone 
Concept of smart modern luxury wealthy home. On white wall home security alarm and video intercom with street view talkback or doorphone voice communications system close up, no people 
Office IP telephone with LCD. VOIP Telephony multi function. isolated on white background 
intercom video door bell on the wall outside modern dining room 