A big birthday
A voice keepsake for a milestone birthday
The room cannot always fit everyone. Their voices can. For a big birthday, the people who love them each leave a short message, and it lands as one book with their name on it.
You do not need a party for it. A daughter in Cork, a brother in Boston, an old friend who cannot travel. Each records a minute, and none of them have to be in the same room.
They open it on the day, hear every voice, and keep it long after the cake is gone.