[dustmite]

Well,

They've all worked out what it's for, as they can hear the music. It's not sound proof. They worked out that the door is there (as you can see from Tania and Nush sitting, listening through the wall/door in my picture)

The phone is so they can speak to Big Brother, instead of the diary room, they have to pick up the phone, press the eye-button, then wait for the green light above it.