Geez... Could they just use a cellphone to call to each other (flight crew and pilots)...
Wouldn't this be part of the troubleshooting guide?
I get that after 9/11 - you ignore the pounding on the door... but if your contact method on the plane between flight crew and flight deck... wouldn't you have some alternate - like say cell phone? --- OR even pilot to cabin radio... and maybe a cabin microphone?
https://currently.att.yahoo.com/news/articles/plane-makes-emergency-landing-pilots-022501623.html