July 2020. ProCall 7 Enterprise 

You can activate "Hold call" during a call in the ProCall Mobile app for iOS simply by pressing and holding the microphone button (mute button).To retrieve the call from Hold, press the Call Hold key (Pause key). 

Function availability

The availability of the function depends on the iOS version, system environment, configuration and the supported features of the telephone system. In ProCall Enterprise the function is released from version 7.0.12 of the Mobile App and from version 7.0.1 of ProCall 7 Enterprise.