sorry you didn't get a fair answer
so
in order to be heard by other planes or radio receivers, you have to key your microphone. the british seem to call the radio, the radio telephone or "RT".
we just call it the radio here.
SO you don't push the button and NOTHING is heard beyond the guy next to you in the cockpit...unless you are loud and the plane is quiet in which case the flight attendants or first class passengers might just hear your voice.
Some planes do require sort of an intercom between the pilots. Some are voice activated in which case you select intercom or RT...indeed in some cases you can switch the buttons back and forth
and to further confuse things, there is a button (on some planes) to ac tivate the public address ssystem so the passengers can hear you say something witty.
Other planes have a little telephone handset for the PA system or interphone to the flight attendants, and it is different than the radio headset you might use over the radio...this is so YOU DO NOT SCREW UP AND SAY: BOSTON CENTER THIS IS >>>> and the passengers hear you.
good luck and ignore the ill will of some