Furuno LH-5000 Operator's Manual page 31

Press and hold the PTT key on the microphone to answer the call in
ALL mode.
The LH-5000 automatically switches to the calling intercom speaker.
After completing your conversation, press the ALL key to return to
the home screen, or press the same selected key (IC1-IC6) to back to
previous mode.
When multiple incoming calls arrive simultaneously, the LH-5000
automatically handles the call in ascending order of the intercom station
number. For example, the LH-5000 receives calls from IC1 and IC 5 at the
same time, it will handle the call from IC1 first and then the call from IC 5.
In the home screen, press and hold the PTT key on the microphone to
answer the call.
The LH-5000 automatically receives the call from the speaker whose
number is the smallest.
After completing your conversation, press the ALL key to return to
the home screen.
Press and hold the PTT key again on the microphone again.
The LH-5000 automatically receives the call from another speaker
whose number is the smaller.