Calls: Mute but no Hold
For active calls, there is a "Mute" button, which presumably means to stop sending audio to the other party, and possibly receiving audio from them. In telephony there is also a "Hold" function which is a PSTN operation where the call is not disconnected but audio is neither sent nor received. In some systems, the network sends an audio stream while a party is on hold, like music.
They are separate functions that need to be dealt with.